diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 15392278c9..fbd8507193 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -51,7 +51,7 @@ jobs:
     inputs:
       actions: 'build'
       scheme: ''
-      sdk: 'macosx11.0'
+      sdk: 'macosx11.1'
       configuration: 'Release'
       xcWorkspacePath: '**/*.xcodeproj/project.xcworkspace'
       xcodeVersion: '12' # Options: 8, 9, default, specifyPath
diff --git a/build/SharedVersion.props b/build/SharedVersion.props
index 43ec995ed9..9a268a21e7 100644
--- a/build/SharedVersion.props
+++ b/build/SharedVersion.props
@@ -21,6 +21,6 @@
   </PropertyGroup>
 
   <ItemGroup Label="PackageIcon">
-    <None Include="$(MSBuildThisFileDirectory)/Assets/Icon.png" Pack="true" PackagePath=""/>
+    <None Include="$(MSBuildThisFileDirectory)/Assets/Icon.png" Pack="true" Visible="false" PackagePath=""/>
   </ItemGroup>
 </Project>
diff --git a/native/Avalonia.Native/src/OSX/rendertarget.mm b/native/Avalonia.Native/src/OSX/rendertarget.mm
index 00b6dab219..b2d4341bb9 100644
--- a/native/Avalonia.Native/src/OSX/rendertarget.mm
+++ b/native/Avalonia.Native/src/OSX/rendertarget.mm
@@ -111,7 +111,11 @@
         if(_renderbuffer != 0)
             glDeleteRenderbuffers(1, &_renderbuffer);
     }
-    CFRelease(surface);
+
+    if(surface != nullptr)
+    {
+        CFRelease(surface);
+    }
 }
 @end
 
@@ -145,6 +149,12 @@ static IAvnGlSurfaceRenderTarget* CreateGlRenderTarget(IOSurfaceRenderTarget* ta
 }
 
 - (void)resize:(AvnPixelSize)size withScale: (float) scale{
+
+    if(size.Height <= 0)
+        size.Height = 1;
+    if(size.Width <= 0)
+        size.Width = 1;
+
     @synchronized (lock) {
         if(surface == nil
            || surface->size.Width != size.Width
diff --git a/src/Avalonia.Controls.DataGrid/DataGrid.cs b/src/Avalonia.Controls.DataGrid/DataGrid.cs
index 5bb2763566..6687c59aa4 100644
--- a/src/Avalonia.Controls.DataGrid/DataGrid.cs
+++ b/src/Avalonia.Controls.DataGrid/DataGrid.cs
@@ -1,6 +1,6 @@
 // This source is subject to the Microsoft Public License (Ms-PL).
 // Please see http://go.microsoft.com/fwlink/?LinkID=131993 for details.
-// All other rights reserved. 
+// All other rights reserved.
 
 using Avalonia.Collections;
 using Avalonia.Controls.Primitives;
@@ -92,7 +92,7 @@ namespace Avalonia.Controls
         private ContentControl _topRightCornerHeader;
         private Control _frozenColumnScrollBarSpacer;
 
-        // the sum of the widths in pixels of the scrolling columns preceding 
+        // the sum of the widths in pixels of the scrolling columns preceding
         // the first displayed scrolling column
         private double _horizontalOffset;
 
@@ -143,7 +143,7 @@ namespace Avalonia.Controls
         private object _uneditedValue; // Represents the original current cell value at the time it enters editing mode.
         private ICellEditBinding _currentCellEditBinding;
 
-        // An approximation of the sum of the heights in pixels of the scrolling rows preceding 
+        // An approximation of the sum of the heights in pixels of the scrolling rows preceding
         // the first displayed scrolling row.  Since the scrolled off rows are discarded, the grid
         // does not know their actual height. The heights used for the approximation are the ones
         // set as the rows were scrolled off.
@@ -162,7 +162,7 @@ namespace Avalonia.Controls
             AvaloniaProperty.Register<DataGrid, bool>(nameof(CanUserReorderColumns));
 
         /// <summary>
-        /// Gets or sets a value that indicates whether the user can change 
+        /// Gets or sets a value that indicates whether the user can change
         /// the column display order by dragging column headers with the mouse.
         /// </summary>
         public bool CanUserReorderColumns
@@ -247,8 +247,8 @@ namespace Avalonia.Controls
         /// Gets or sets the <see cref="T:System.Windows.Media.Brush" /> that is used to paint the background of odd-numbered rows.
         /// </summary>
         /// <returns>
-        /// The brush that is used to paint the background of odd-numbered rows. The default is a 
-        /// <see cref="T:System.Windows.Media.SolidColorBrush" /> with a 
+        /// The brush that is used to paint the background of odd-numbered rows. The default is a
+        /// <see cref="T:System.Windows.Media.SolidColorBrush" /> with a
         /// <see cref="P:System.Windows.Media.SolidColorBrush.Color" /> value of white (ARGB value #00FFFFFF).
         /// </returns>
         public IBrush AlternatingRowBackground
@@ -379,8 +379,8 @@ namespace Avalonia.Controls
         public bool IsValid
         {
             get { return _isValid; }
-            internal set 
-            { 
+            internal set
+            {
                 SetAndRaise(IsValidProperty, ref _isValid, value);
                 PseudoClasses.Set(":invalid", !value);
             }
@@ -398,7 +398,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Gets or sets the maximum width of columns in the <see cref="T:Avalonia.Controls.DataGrid" /> . 
+        /// Gets or sets the maximum width of columns in the <see cref="T:Avalonia.Controls.DataGrid" /> .
         /// </summary>
         public double MaxColumnWidth
         {
@@ -418,7 +418,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Gets or sets the minimum width of columns in the <see cref="T:Avalonia.Controls.DataGrid" />. 
+        /// Gets or sets the minimum width of columns in the <see cref="T:Avalonia.Controls.DataGrid" />.
         /// </summary>
         public double MinColumnWidth
         {
@@ -496,7 +496,7 @@ namespace Avalonia.Controls
             AvaloniaProperty.Register<DataGrid, IBrush>(nameof(VerticalGridLinesBrush));
 
         /// <summary>
-        /// Gets or sets the <see cref="T:System.Windows.Media.Brush" /> that is used to paint grid lines separating columns. 
+        /// Gets or sets the <see cref="T:System.Windows.Media.Brush" /> that is used to paint grid lines separating columns.
         /// </summary>
         public IBrush VerticalGridLinesBrush
         {
@@ -542,7 +542,7 @@ namespace Avalonia.Controls
         /// </summary>
         /// <returns>
         /// The index of the current selection, or -1 if the selection is empty.
-        /// </returns> 
+        /// </returns>
         public int SelectedIndex
         {
             get { return _selectedIndex; }
@@ -582,7 +582,7 @@ namespace Avalonia.Controls
             AvaloniaProperty.Register<DataGrid, bool>(nameof(AutoGenerateColumns));
 
         /// <summary>
-        /// Gets or sets a value that indicates whether columns are created 
+        /// Gets or sets a value that indicates whether columns are created
         /// automatically when the <see cref="P:Avalonia.Controls.DataGrid.ItemsSource" /> property is set.
         /// </summary>
         public bool AutoGenerateColumns
@@ -626,7 +626,7 @@ namespace Avalonia.Controls
             AvaloniaProperty.Register<DataGrid, bool>(nameof(AreRowDetailsFrozen));
 
         /// <summary>
-        /// Gets or sets a value that indicates whether the row details sections remain 
+        /// Gets or sets a value that indicates whether the row details sections remain
         /// fixed at the width of the display area or can scroll horizontally.
         /// </summary>
         public bool AreRowDetailsFrozen
@@ -881,7 +881,7 @@ namespace Avalonia.Controls
             {
                 int index = (int)e.NewValue;
 
-                // GetDataItem returns null if index is >= Count, we do not check newValue 
+                // GetDataItem returns null if index is >= Count, we do not check newValue
                 // against Count here to avoid enumerating through an Enumerable twice
                 // Setting SelectedItem coerces the finally value of the SelectedIndex
                 object newSelectedItem = (index < 0) ? null : DataConnection.GetDataItem(index);
@@ -1168,14 +1168,14 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Occurs one time for each public, non-static property in the bound data type when the 
-        /// <see cref="P:Avalonia.Controls.DataGrid.ItemsSource" /> property is changed and the 
+        /// Occurs one time for each public, non-static property in the bound data type when the
+        /// <see cref="P:Avalonia.Controls.DataGrid.ItemsSource" /> property is changed and the
         /// <see cref="P:Avalonia.Controls.DataGrid.AutoGenerateColumns" /> property is true.
         /// </summary>
         public event EventHandler<DataGridAutoGeneratingColumnEventArgs> AutoGeneratingColumn;
 
         /// <summary>
-        /// Occurs before a cell or row enters editing mode. 
+        /// Occurs before a cell or row enters editing mode.
         /// </summary>
         public event EventHandler<DataGridBeginningEditEventArgs> BeginningEdit;
 
@@ -1195,7 +1195,7 @@ namespace Avalonia.Controls
         public event EventHandler<DataGridCellPointerPressedEventArgs> CellPointerPressed;
 
         /// <summary>
-        /// Occurs when the <see cref="P:Avalonia.Controls.DataGridColumn.DisplayIndex" /> 
+        /// Occurs when the <see cref="P:Avalonia.Controls.DataGridColumn.DisplayIndex" />
         /// property of a column changes.
         /// </summary>
         public event EventHandler<DataGridColumnEventArgs> ColumnDisplayIndexChanged;
@@ -1218,14 +1218,14 @@ namespace Avalonia.Controls
         public event EventHandler<EventArgs> CurrentCellChanged;
 
         /// <summary>
-        /// Occurs after a <see cref="T:Avalonia.Controls.DataGridRow" /> 
+        /// Occurs after a <see cref="T:Avalonia.Controls.DataGridRow" />
         /// is instantiated, so that you can customize it before it is used.
         /// </summary>
         public event EventHandler<DataGridRowEventArgs> LoadingRow;
 
         /// <summary>
         /// Occurs when a cell in a <see cref="T:Avalonia.Controls.DataGridTemplateColumn" /> enters editing mode.
-        /// 
+        ///
         /// </summary>
         public event EventHandler<DataGridPreparingCellForEditEventArgs> PreparingCellForEdit;
 
@@ -1243,7 +1243,7 @@ namespace Avalonia.Controls
             RoutedEvent.Register<DataGrid, SelectionChangedEventArgs>(nameof(SelectionChanged), RoutingStrategies.Bubble);
 
         /// <summary>
-        /// Occurs when the <see cref="P:Avalonia.Controls.DataGrid.SelectedItem" /> or 
+        /// Occurs when the <see cref="P:Avalonia.Controls.DataGrid.SelectedItem" /> or
         /// <see cref="P:Avalonia.Controls.DataGrid.SelectedItems" /> property value changes.
         /// </summary>
         public event EventHandler<SelectionChangedEventArgs> SelectionChanged
@@ -1258,19 +1258,19 @@ namespace Avalonia.Controls
         public event EventHandler<DataGridColumnEventArgs> Sorting;
 
         /// <summary>
-        /// Occurs when a <see cref="T:Avalonia.Controls.DataGridRow" /> 
+        /// Occurs when a <see cref="T:Avalonia.Controls.DataGridRow" />
         /// object becomes available for reuse.
         /// </summary>
         public event EventHandler<DataGridRowEventArgs> UnloadingRow;
 
         /// <summary>
-        /// Occurs when a new row details template is applied to a row, so that you can customize 
+        /// Occurs when a new row details template is applied to a row, so that you can customize
         /// the details section before it is used.
         /// </summary>
         public event EventHandler<DataGridRowDetailsEventArgs> LoadingRowDetails;
 
         /// <summary>
-        /// Occurs when the <see cref="P:Avalonia.Controls.DataGrid.RowDetailsVisibilityMode" /> 
+        /// Occurs when the <see cref="P:Avalonia.Controls.DataGrid.RowDetailsVisibilityMode" />
         /// property value changes.
         /// </summary>
         public event EventHandler<DataGridRowDetailsEventArgs> RowDetailsVisibilityChanged;
@@ -1282,7 +1282,7 @@ namespace Avalonia.Controls
 
         /// <summary>
         /// Gets a collection that contains all the columns in the control.
-        /// </summary>      
+        /// </summary>
         public ObservableCollection<DataGridColumn> Columns
         {
             get
@@ -1456,7 +1456,7 @@ namespace Avalonia.Controls
         }
 
         // Height currently available for cells this value is smaller.  This height is reduced by the existence of ColumnHeaders
-        // or a horizontal scrollbar.  Layout is asynchronous so changes to the ColumnHeaders or the horizontal scrollbar are 
+        // or a horizontal scrollbar.  Layout is asynchronous so changes to the ColumnHeaders or the horizontal scrollbar are
         // not reflected immediately.
         internal double CellsHeight
         {
@@ -1555,7 +1555,7 @@ namespace Avalonia.Controls
 
         internal static double HorizontalGridLinesThickness => DATAGRID_horizontalGridLinesThickness;
 
-        // the sum of the widths in pixels of the scrolling columns preceding 
+        // the sum of the widths in pixels of the scrolling columns preceding
         // the first displayed scrolling column
         internal double HorizontalOffset
         {
@@ -2083,20 +2083,20 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Measures the children of a <see cref="T:Avalonia.Controls.DataGridRow" /> to prepare for 
-        /// arranging them during the 
-        /// <see cref="M:Avalonia.Controls.DataGridRow.ArrangeOverride(System.Windows.Size)" /> pass. 
+        /// Measures the children of a <see cref="T:Avalonia.Controls.DataGridRow" /> to prepare for
+        /// arranging them during the
+        /// <see cref="M:Avalonia.Controls.DataGridRow.ArrangeOverride(System.Windows.Size)" /> pass.
         /// </summary>
         /// <returns>
         /// The size that the <see cref="T:Avalonia.Controls.DataGridRow" /> determines it needs during layout, based on its calculations of child object allocated sizes.
         /// </returns>
         /// <param name="availableSize">
-        /// The available size that this element can give to child elements. Indicates an upper limit that 
+        /// The available size that this element can give to child elements. Indicates an upper limit that
         /// child elements should not exceed.
         /// </param>
         protected override Size MeasureOverride(Size availableSize)
         {
-            // Delay layout until after the initial measure to avoid invalid calculations when the 
+            // Delay layout until after the initial measure to avoid invalid calculations when the
             // DataGrid is not part of the visual tree
             if (!_measured)
             {
@@ -3006,7 +3006,7 @@ namespace Avalonia.Controls
         /// If the editing element has focus, this method will set focus to the DataGrid itself
         /// in order to force the element to lose focus.  It will then wait for the editing element's
         /// LostFocus event, at which point it will perform the specified action.
-        /// 
+        ///
         /// NOTE: It is important to understand that the specified action will be performed when the editing
         /// element loses focus only if this method returns true.  If it returns false, then the action
         /// will not be performed later on, and should instead be performed by the caller, if necessary.
@@ -3065,7 +3065,7 @@ namespace Avalonia.Controls
         {
             if (!_scrollingByHeight)
             {
-                // Update layout when RowDetails are expanded or collapsed, just updating the vertical scroll bar is not enough 
+                // Update layout when RowDetails are expanded or collapsed, just updating the vertical scroll bar is not enough
                 // since rows could be added or removed
                 InvalidateMeasure();
             }
@@ -3278,7 +3278,7 @@ namespace Avalonia.Controls
             {
                 // Current cell was reset because the commit deleted row(s).
                 // Since the user wants to change the current cell, we don't
-                // want to end up with no current cell. We pick the last row 
+                // want to end up with no current cell. We pick the last row
                 // in the grid which may be the 'new row'.
                 int lastSlot = LastVisibleSlot;
                 if (forCurrentCellChange &&
@@ -3336,7 +3336,7 @@ namespace Avalonia.Controls
             if (_ignoreNextScrollBarsLayout)
             {
                 _ignoreNextScrollBarsLayout = false;
-                //  
+                //
 
             }
 
@@ -3393,7 +3393,7 @@ namespace Avalonia.Controls
             }
 
             // Now cellsWidth is the width potentially available for displaying data cells.
-            // Now cellsHeight is the height potentially available for displaying data cells. 
+            // Now cellsHeight is the height potentially available for displaying data cells.
 
             bool needHorizScrollbar = false;
             bool needVertScrollbar = false;
@@ -3418,7 +3418,7 @@ namespace Avalonia.Controls
                     Debug.Assert(cellsHeight >= 0);
                     needHorizScrollbarWithoutVertScrollbar = needHorizScrollbar = true;
 
-                    if (vertScrollBarWidth > 0 && 
+                    if (vertScrollBarWidth > 0 &&
                         allowVertScrollbar && (MathUtilities.LessThanOrClose(totalVisibleWidth - cellsWidth, vertScrollBarWidth) ||
                         MathUtilities.LessThanOrClose(cellsWidth - totalVisibleFrozenWidth, vertScrollBarWidth)))
                     {
@@ -3458,7 +3458,7 @@ namespace Avalonia.Controls
                 // we compute the number of visible columns only after we set up the vertical scroll bar.
                 ComputeDisplayedColumns();
 
-                if ((vertScrollBarWidth > 0 || horizScrollBarHeight > 0) && 
+                if ((vertScrollBarWidth > 0 || horizScrollBarHeight > 0) &&
                     allowHorizScrollbar &&
                     needVertScrollbar && !needHorizScrollbar &&
                     MathUtilities.GreaterThan(totalVisibleWidth, cellsWidth) &&
@@ -3963,7 +3963,8 @@ namespace Avalonia.Controls
                         {
                             var errorList =
                                 binding.ValidationErrors
-                                       .SelectMany(ex => ValidationUtil.UnpackException(ex))
+                                       .SelectMany(ValidationUtil.UnpackException)
+                                       .Select(ValidationUtil.UnpackDataValidationException)
                                        .ToList();
 
                             DataValidationErrors.SetErrors(editingElement, errorList);
@@ -4124,7 +4125,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Exits editing mode without trying to commit or revert the editing, and 
+        /// Exits editing mode without trying to commit or revert the editing, and
         /// without repopulating the edited row's cell.
         /// </summary>
         //TODO TabStop
@@ -5103,9 +5104,9 @@ namespace Avalonia.Controls
         {
             if (ctrl || _editingColumnIndex == -1 || IsReadOnly)
             {
-                //Go to the next/previous control on the page when 
+                //Go to the next/previous control on the page when
                 // - Ctrl key is used
-                // - Potential current cell is not edited, or the datagrid is read-only. 
+                // - Potential current cell is not edited, or the datagrid is read-only.
                 return false;
             }
 
@@ -5516,11 +5517,11 @@ namespace Avalonia.Controls
                     //        v---v
                     //|<|_____|###|>|
                     //  ^     ^
-                    //  min   max 
+                    //  min   max
 
                     // we want to make the relative size of the thumb reflect the relative size of the viewing area
                     // viewportSize / (max + viewportSize) = cellsWidth / max
-                    // -> viewportSize = max * cellsWidth / (max - cellsWidth) 
+                    // -> viewportSize = max * cellsWidth / (max - cellsWidth)
 
                     // always zero
                     _hScrollBar.Minimum = 0;
@@ -5572,7 +5573,7 @@ namespace Avalonia.Controls
                     _hScrollBar.Maximum = 0;
                     if (_hScrollBar.IsVisible)
                     {
-                        // This will trigger a call to this method via Cells_SizeChanged for 
+                        // This will trigger a call to this method via Cells_SizeChanged for
                         // which no processing is needed.
                         _hScrollBar.IsVisible = false;
                         _ignoreNextScrollBarsLayout = true;
@@ -5591,14 +5592,14 @@ namespace Avalonia.Controls
                     //        v---v
                     //|<|_____|###|>|
                     //  ^     ^
-                    //  min   max 
+                    //  min   max
 
                     // we want to make the relative size of the thumb reflect the relative size of the viewing area
                     // viewportSize / (max + viewportSize) = cellsWidth / max
                     // -> viewportSize = max * cellsHeight / (totalVisibleHeight - cellsHeight)
                     // ->              = max * cellsHeight / (totalVisibleHeight - cellsHeight)
                     // ->              = max * cellsHeight / max
-                    // ->              = cellsHeight 
+                    // ->              = cellsHeight
 
                     // always zero
                     _vScrollBar.Minimum = 0;
@@ -5621,7 +5622,7 @@ namespace Avalonia.Controls
 
                     if (!_vScrollBar.IsVisible)
                     {
-                        // This will trigger a call to this method via Cells_SizeChanged for 
+                        // This will trigger a call to this method via Cells_SizeChanged for
                         // which no processing is needed.
                         _vScrollBar.IsVisible = true;
                         if (_vScrollBar.DesiredSize.Width == 0)
@@ -5637,7 +5638,7 @@ namespace Avalonia.Controls
                     _vScrollBar.Maximum = 0;
                     if (_vScrollBar.IsVisible)
                     {
-                        // This will trigger a call to this method via Cells_SizeChanged for 
+                        // This will trigger a call to this method via Cells_SizeChanged for
                         // which no processing is needed.
                         _vScrollBar.IsVisible = false;
                         _ignoreNextScrollBarsLayout = true;
@@ -5660,8 +5661,8 @@ namespace Avalonia.Controls
             Debug.Assert(slot >= 0);
 
             // Before changing selection, check if the current cell needs to be committed, and
-            // check if the current row needs to be committed. If any of those two operations are required and fail, 
-            // do not change selection, and do not change current cell. 
+            // check if the current row needs to be committed. If any of those two operations are required and fail,
+            // do not change selection, and do not change current cell.
 
             bool wasInEdit = EditingColumnIndex != -1;
 
diff --git a/src/Avalonia.Controls.DataGrid/Utils/ValidationUtil.cs b/src/Avalonia.Controls.DataGrid/Utils/ValidationUtil.cs
index e1ecb2c562..c36d9708c1 100644
--- a/src/Avalonia.Controls.DataGrid/Utils/ValidationUtil.cs
+++ b/src/Avalonia.Controls.DataGrid/Utils/ValidationUtil.cs
@@ -80,19 +80,24 @@ namespace Avalonia.Controls.Utils
         {
             if (exception != null)
             {
-                var aggregate = exception as AggregateException;
-                var exceptions = aggregate == null ?
-                    (IEnumerable<Exception>)new[] { exception } :
-                    aggregate.InnerExceptions;
-                var filtered = exceptions.Where(x => !(x is BindingChainException)).ToList();
+                var exceptions = exception is AggregateException aggregate ?
+                    aggregate.InnerExceptions :
+                    (IEnumerable<Exception>)new[] { exception };
 
-                if (filtered.Count > 0)
-                {
-                    return filtered;
-                }
+                return exceptions.Where(x => !(x is BindingChainException)).ToList();
             }
 
-            return null;
+            return Array.Empty<Exception>();
+        }
+
+        public static object UnpackDataValidationException(Exception exception)
+        {
+            if (exception is DataValidationException dataValidationException)
+            {
+                return dataValidationException.ErrorData;
+            }
+
+            return exception;
         }
 
         /// <summary>
diff --git a/src/Avalonia.Controls/ContextMenu.cs b/src/Avalonia.Controls/ContextMenu.cs
index 5e17182f3e..fb8080f0d4 100644
--- a/src/Avalonia.Controls/ContextMenu.cs
+++ b/src/Avalonia.Controls/ContextMenu.cs
@@ -246,7 +246,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Opens the menu.
         /// </summary>
-        public override void Open() => throw new NotSupportedException();
+        public override void Open() => Open(null);
 
         /// <summary>
         /// Opens a context menu on the specified control.
diff --git a/src/Avalonia.Layout/ElementManager.cs b/src/Avalonia.Layout/ElementManager.cs
index 70805ba31c..bf5a45966b 100644
--- a/src/Avalonia.Layout/ElementManager.cs
+++ b/src/Avalonia.Layout/ElementManager.cs
@@ -129,7 +129,7 @@ namespace Avalonia.Layout
         {
             for (int i = 0; i < count; i++)
             {
-                // Clear from the edges so that ItemsRepeater can optimize on maintaining 
+                // Clear from the edges so that ItemsRepeater can optimize on maintaining
                 // realized indices without walking through all the children every time.
                 int index = realizedIndex == 0 ? realizedIndex + i : (realizedIndex + count - 1) - i;
                 var elementRef = _realizedElements[index];
@@ -212,7 +212,7 @@ namespace Avalonia.Layout
         public ILayoutable GetRealizedElement(int dataIndex)
         {
             return IsVirtualizingContext ?
-                GetAt(GetRealizedRangeIndexFromDataIndex(dataIndex)) : 
+                GetAt(GetRealizedRangeIndexFromDataIndex(dataIndex)) :
                 _context.GetOrCreateElementAt(
                     dataIndex,
                     ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
@@ -252,7 +252,6 @@ namespace Avalonia.Layout
                     (orientation == ScrollOrientation.Vertical ? ScrollOrientation.Horizontal : ScrollOrientation.Vertical) :
                     orientation;
 
-
                 var windowStart = effectiveOrientation == ScrollOrientation.Vertical ? window.Y : window.X;
                 var windowEnd = effectiveOrientation == ScrollOrientation.Vertical ? window.Y + window.Height : window.X + window.Width;
                 var firstElementStart = effectiveOrientation == ScrollOrientation.Vertical ? firstElementBounds.Y : firstElementBounds.X;
@@ -273,53 +272,53 @@ namespace Avalonia.Layout
                 switch (args.Action)
                 {
                     case NotifyCollectionChangedAction.Add:
-                    {
-                        OnItemsAdded(args.NewStartingIndex, args.NewItems.Count);
-                    }
-                    break;
+                        {
+                            OnItemsAdded(args.NewStartingIndex, args.NewItems.Count);
+                        }
+                        break;
 
                     case NotifyCollectionChangedAction.Replace:
-                    {
-                        int oldSize = args.OldItems.Count;
-                        int newSize = args.NewItems.Count;
-                        int oldStartIndex = args.OldStartingIndex;
-                        int newStartIndex = args.NewStartingIndex;
-
-                        if (oldSize == newSize &&
-                            oldStartIndex == newStartIndex &&
-                            IsDataIndexRealized(oldStartIndex) &&
-                            IsDataIndexRealized(oldStartIndex + oldSize -1))
                         {
-                            // Straight up replace of n items within the realization window.
-                            // Removing and adding might causes us to lose the anchor causing us
-                            // to throw away all containers and start from scratch.
-                            // Instead, we can just clear those items and set the element to
-                            // null (sentinel) and let the next measure get new containers for them.
-                            var startRealizedIndex = GetRealizedRangeIndexFromDataIndex(oldStartIndex);
-                            for (int realizedIndex = startRealizedIndex; realizedIndex < startRealizedIndex + oldSize; realizedIndex++)
+                            int oldSize = args.OldItems.Count;
+                            int newSize = args.NewItems.Count;
+                            int oldStartIndex = args.OldStartingIndex;
+                            int newStartIndex = args.NewStartingIndex;
+
+                            if (oldSize == newSize &&
+                                oldStartIndex == newStartIndex &&
+                                IsDataIndexRealized(oldStartIndex) &&
+                                IsDataIndexRealized(oldStartIndex + oldSize - 1))
                             {
-                                var elementRef = _realizedElements[realizedIndex];
-
-                                if (elementRef != null)
+                                // Straight up replace of n items within the realization window.
+                                // Removing and adding might causes us to lose the anchor causing us
+                                // to throw away all containers and start from scratch.
+                                // Instead, we can just clear those items and set the element to
+                                // null (sentinel) and let the next measure get new containers for them.
+                                var startRealizedIndex = GetRealizedRangeIndexFromDataIndex(oldStartIndex);
+                                for (int realizedIndex = startRealizedIndex; realizedIndex < startRealizedIndex + oldSize; realizedIndex++)
                                 {
-                                    _context.RecycleElement(elementRef);
-                                    _realizedElements[realizedIndex] = null;
+                                    var elementRef = _realizedElements[realizedIndex];
+
+                                    if (elementRef != null)
+                                    {
+                                        _context.RecycleElement(elementRef);
+                                        _realizedElements[realizedIndex] = null;
+                                    }
                                 }
                             }
+                            else
+                            {
+                                OnItemsRemoved(oldStartIndex, oldSize);
+                                OnItemsAdded(newStartIndex, newSize);
+                            }
                         }
-                        else
-                        {
-                            OnItemsRemoved(oldStartIndex, oldSize);
-                            OnItemsAdded(newStartIndex, newSize);
-                        }
-                    }
-                    break;
+                        break;
 
                     case NotifyCollectionChangedAction.Remove:
-                    {
-                        OnItemsRemoved(args.OldStartingIndex, args.OldItems.Count);
-                    }
-                    break;
+                        {
+                            OnItemsRemoved(args.OldStartingIndex, args.OldItems.Count);
+                        }
+                        break;
 
                     case NotifyCollectionChangedAction.Reset:
                         ClearRealizedRange();
@@ -376,7 +375,7 @@ namespace Avalonia.Layout
             int backCutoffIndex = realizedRangeSize;
 
             for (int i = 0;
-                i<realizedRangeSize &&
+                i < realizedRangeSize &&
                 !Intersects(window, _realizedElementLayoutBounds[i], orientation);
                 ++i)
             {
@@ -391,7 +390,7 @@ namespace Avalonia.Layout
                 --backCutoffIndex;
             }
 
-            if (backCutoffIndex<realizedRangeSize - 1)
+            if (backCutoffIndex < realizedRangeSize - 1)
             {
                 ClearRealizedRange(backCutoffIndex + 1, realizedRangeSize - backCutoffIndex - 1);
             }
@@ -419,14 +418,14 @@ namespace Avalonia.Layout
             // to insert items.
             int lastRealizedDataIndex = _firstRealizedDataIndex + GetRealizedElementCount() - 1;
             int newStartingIndex = index;
-            if (newStartingIndex > _firstRealizedDataIndex &&
+            if (newStartingIndex >= _firstRealizedDataIndex &&
                 newStartingIndex <= lastRealizedDataIndex)
             {
                 // Inserted within the realized range
                 int insertRangeStartIndex = newStartingIndex - _firstRealizedDataIndex;
                 for (int i = 0; i < count; i++)
                 {
-                    // Insert null (sentinel) here instead of an element, that way we dont 
+                    // Insert null (sentinel) here instead of an element, that way we dont
                     // end up creating a lot of elements only to be thrown out in the next layout.
                     int insertRangeIndex = insertRangeStartIndex + i;
                     int dataIndex = newStartingIndex + i;
diff --git a/src/Avalonia.Themes.Fluent/Controls/Expander.xaml b/src/Avalonia.Themes.Fluent/Controls/Expander.xaml
index 97ca62c493..ad0fd18ea5 100644
--- a/src/Avalonia.Themes.Fluent/Controls/Expander.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/Expander.xaml
@@ -108,7 +108,7 @@
     </Setter>
   </Style>
   <Style Selector="Expander /template/ ToggleButton#PART_toggle:pointerover /template/ Border">
-    <Setter Property="BorderBrush" Value="{DynamicResource SystemControlTransientBorderBrush}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource SystemControlHighlightBaseMediumBrush}" />
   </Style>
   <Style Selector="Expander:down:expanded /template/ ToggleButton#PART_toggle /template/ Path">
     <Setter Property="RenderTransform">
diff --git a/src/Avalonia.X11/X11Atoms.cs b/src/Avalonia.X11/X11Atoms.cs
index 32f1822e51..137757b9cf 100644
--- a/src/Avalonia.X11/X11Atoms.cs
+++ b/src/Avalonia.X11/X11Atoms.cs
@@ -114,6 +114,8 @@ namespace Avalonia.X11
         public readonly IntPtr XA_WM_CLASS = (IntPtr)67;
         public readonly IntPtr XA_WM_TRANSIENT_FOR = (IntPtr)68;
 
+        public readonly IntPtr RR_PROPERTY_RANDR_EDID = (IntPtr)82;
+
         public readonly IntPtr WM_PROTOCOLS;
         public readonly IntPtr WM_DELETE_WINDOW;
         public readonly IntPtr WM_TAKE_FOCUS;
diff --git a/src/Avalonia.X11/X11Screens.cs b/src/Avalonia.X11/X11Screens.cs
index af6d2674b6..b51497fb13 100644
--- a/src/Avalonia.X11/X11Screens.cs
+++ b/src/Avalonia.X11/X11Screens.cs
@@ -66,7 +66,8 @@ namespace Avalonia.X11
             private X11Screen[] _cache;
             private X11Info _x11;
             private IntPtr _window;
-
+            const int EDIDStructureLength = 32; // Length of a EDID-Block-Length(128 bytes), XRRGetOutputProperty multiplies offset and length by 4
+            
             public Randr15ScreensImpl(AvaloniaX11Platform platform, X11ScreensUserSettings settings)
             {
                 _settings = settings;
@@ -82,6 +83,38 @@ namespace Avalonia.X11
                     _cache = null;
             }
 
+            private unsafe Size? GetPhysicalMonitorSizeFromEDID(IntPtr rrOutput)
+            {
+                if(rrOutput == IntPtr.Zero)
+                    return null;
+                var properties = XRRListOutputProperties(_x11.Display,rrOutput, out int propertyCount);
+                var hasEDID = false;
+                for(var pc = 0; pc < propertyCount; pc++)
+                {
+                    if(properties[pc] == _x11.Atoms.RR_PROPERTY_RANDR_EDID)
+                        hasEDID = true;
+                }
+                if(!hasEDID)
+                    return null;
+                XRRGetOutputProperty(_x11.Display, rrOutput, _x11.Atoms.RR_PROPERTY_RANDR_EDID, 0, EDIDStructureLength, false, false, _x11.Atoms.AnyPropertyType, out IntPtr actualType, out int actualFormat, out int bytesAfter, out _, out IntPtr prop);
+                if(actualType != _x11.Atoms.XA_INTEGER)
+                    return null;
+                if(actualFormat != 8) // Expecting an byte array
+                    return null;
+
+                var edid = new byte[bytesAfter];
+                Marshal.Copy(prop,edid,0,bytesAfter);
+                XFree(prop);
+                XFree(new IntPtr(properties));
+                if(edid.Length < 22)
+                    return null;
+                var width = edid[21]; // 0x15 1 Max. Horizontal Image Size cm. 
+                var height = edid[22]; // 0x16 1 Max. Vertical Image Size cm. 
+                if(width == 0 && height == 0)
+                    return null;
+                return new Size(width * 10, height * 10);
+            }
+
             public unsafe X11Screen[] Screens
             {
                 get
@@ -97,24 +130,28 @@ namespace Avalonia.X11
                         var namePtr = XGetAtomName(_x11.Display, mon.Name);
                         var name = Marshal.PtrToStringAnsi(namePtr);
                         XFree(namePtr);
-
-                        var density = 1d;
+                        var bounds = new PixelRect(mon.X, mon.Y, mon.Width, mon.Height);
+                        Size? pSize = null;
+                        double density = 0;
                         if (_settings.NamedScaleFactors?.TryGetValue(name, out density) != true)
                         {
-                            if (mon.MWidth == 0)
-                                density = 1;
-                            else
-                                density = X11Screen.GuessPixelDensity(mon.Width, mon.MWidth);
+                            for(int o = 0; o < mon.NOutput; o++)
+                            {
+                                var outputSize = GetPhysicalMonitorSizeFromEDID(mon.Outputs[o]);
+                                var outputDensity = 1d;
+                                if(outputSize != null)
+                                    outputDensity = X11Screen.GuessPixelDensity(bounds, outputSize.Value);
+                                if(density == 0 || density > outputDensity)
+                                {
+                                    density = outputDensity;
+                                    pSize = outputSize;
+                                }
+                            }
                         }
-
+                        if(density == 0)
+                            density = 1;
                         density *= _settings.GlobalScaleFactor;
-                        
-                        var bounds = new PixelRect(mon.X, mon.Y, mon.Width, mon.Height);
-                        screens[c] = new X11Screen(bounds, 
-                            mon.Primary != 0, 
-                            name,
-                            (mon.MWidth == 0 || mon.MHeight == 0) ? (Size?)null : new Size(mon.MWidth, mon.MHeight),
-                            density);
+                        screens[c] = new X11Screen(bounds, mon.Primary != 0, name, pSize, density);
                     }
                     
                     XFree(new IntPtr(monitors));
@@ -163,7 +200,6 @@ namespace Avalonia.X11
 
         }
 
-
         public int ScreenCount => _impl.Screens.Length;
 
         public IReadOnlyList<Screen> AllScreens =>
@@ -229,6 +265,7 @@ namespace Avalonia.X11
     class X11Screen
     {
         private const int FullHDWidth = 1920;
+        private const int FullHDHeight = 1080;
         public bool Primary { get; }
         public string Name { get; set; }
         public PixelRect Bounds { get; set; }
@@ -248,7 +285,7 @@ namespace Avalonia.X11
             }
             else if (pixelDensity == null)
             {
-                PixelDensity = GuessPixelDensity(bounds.Width, physicalSize.Value.Width);
+                PixelDensity = GuessPixelDensity(bounds, physicalSize.Value);
             }
             else
             {
@@ -257,7 +294,26 @@ namespace Avalonia.X11
             }
         }
 
-        public static double GuessPixelDensity(double pixelWidth, double mmWidth)
-            => pixelWidth <= FullHDWidth ? 1 : Math.Max(1, Math.Round(pixelWidth / mmWidth * 25.4 / 96));
+        public static double GuessPixelDensity(PixelRect pixel, Size physical)
+        {
+            var calculatedDensity = 1d;
+            if(physical.Width > 0)
+                calculatedDensity = pixel.Width <= FullHDWidth ? 1 : Math.Max(1, pixel.Width / physical.Width * 25.4 / 96);
+            else if(physical.Height > 0)
+                calculatedDensity = pixel.Height <= FullHDHeight ? 1 : Math.Max(1, pixel.Height / physical.Height * 25.4 / 96);
+            
+            if(calculatedDensity > 3)
+                return 1;
+            else
+            {
+                var sanePixelDensities = new double[] { 1, 1.25, 1.50, 1.75, 2 };
+                foreach(var saneDensity in sanePixelDensities)
+                {
+                    if(calculatedDensity <= saneDensity + 0.20)
+                        return saneDensity;
+                }
+                return sanePixelDensities.Last();
+            }
+        }
     }
 }
diff --git a/src/Avalonia.X11/X11Structs.cs b/src/Avalonia.X11/X11Structs.cs
index 0ae5c16aef..ae4954a2d5 100644
--- a/src/Avalonia.X11/X11Structs.cs
+++ b/src/Avalonia.X11/X11Structs.cs
@@ -1870,7 +1870,7 @@ namespace Avalonia.X11 {
 		public const string XNFontSet = "fontSet";
 	}
 	
-    struct XRRMonitorInfo {
+    unsafe struct XRRMonitorInfo {
         public IntPtr Name;
         public int Primary;
         public int Automatic;
@@ -1881,6 +1881,6 @@ namespace Avalonia.X11 {
         public int Height;
         public int MWidth;
         public int MHeight;
-        public IntPtr Outputs;
+        public IntPtr* Outputs;
     } 
 }
diff --git a/src/Avalonia.X11/XLib.cs b/src/Avalonia.X11/XLib.cs
index 85aa4862b7..bec94e63c9 100644
--- a/src/Avalonia.X11/XLib.cs
+++ b/src/Avalonia.X11/XLib.cs
@@ -500,6 +500,13 @@ namespace Avalonia.X11
         [DllImport(libX11Randr)]
         public static extern XRRMonitorInfo*
             XRRGetMonitors(IntPtr dpy, IntPtr window, bool get_active, out int nmonitors);
+
+        [DllImport(libX11Randr)]
+        public static extern IntPtr* XRRListOutputProperties(IntPtr dpy, IntPtr output, out int count);
+
+        [DllImport(libX11Randr)]
+        public static extern int XRRGetOutputProperty(IntPtr dpy, IntPtr output, IntPtr atom, int offset, int length, bool _delete, bool pending, IntPtr req_type, out IntPtr actual_type, out int actual_format, out int nitems, out long bytes_after, out IntPtr prop);
+            
         [DllImport(libX11Randr)]
         public static extern void XRRSelectInput(IntPtr dpy, IntPtr window, RandrEventMask mask);
 
diff --git a/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs b/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
index 39a3250686..f3a1316c7d 100644
--- a/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ContextMenuTests.cs
@@ -44,6 +44,55 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Open_Should_Use_Default_Control()
+        {
+            using (Application())
+            {
+                var sut = new ContextMenu();
+                var target = new Panel
+                {
+                    ContextMenu = sut
+                };
+
+                var window = new Window { Content = target };
+                window.ApplyTemplate();
+                window.Presenter.ApplyTemplate();
+
+                bool opened = false;
+
+                sut.MenuOpened += (sender, args) =>
+                {
+                    opened = true;
+                };
+
+                sut.Open();
+
+                Assert.True(opened);
+            }
+        }
+
+        [Fact]
+        public void Open_Should_Raise_Exception_If_AlreadyDetached()
+        {
+            using (Application())
+            {
+                var sut = new ContextMenu();
+                var target = new Panel
+                {
+                    ContextMenu = sut
+                };
+
+                var window = new Window { Content = target };
+                window.ApplyTemplate();
+                window.Presenter.ApplyTemplate();
+
+                target.ContextMenu = null;
+
+               Assert.ThrowsAny<Exception>(()=> sut.Open());
+            }
+        }
+
         [Fact]
         public void Closing_Raises_Single_Closed_Event()
         {