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/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.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()
         {