Fixed failing test.

src/Perspex.Controls/Presenters/ContentPresenter.cs

@@ -104,8 +104,12 @@ namespace Perspex.Controls.Presenters
             var logicalHost = this.FindReparentingHost();
             var logicalChildren = logicalHost?.LogicalChildren ?? LogicalChildren;
 
-            logicalChildren.Remove(old);
-            ClearVisualChildren();
+            if (old != null)
+            {
+                logicalChildren.Remove(old);
+                ((ISetLogicalParent)old).SetParent(null);
+                ClearVisualChildren();
+            }
 
             Child = result;
 

tests/Perspex.Controls.UnitTests/ContentPresenterTests.cs

@@ -4,6 +4,7 @@
 using System.Collections.Specialized;
 using System.Linq;
 using Perspex.Controls.Presenters;
+using Perspex.LogicalTree;
 using Xunit;
 
 namespace Perspex.Controls.UnitTests
@@ -29,11 +30,28 @@ namespace Perspex.Controls.UnitTests
             var child = new Control();
 
             target.Content = child;
+            target.ApplyTemplate();
             target.Content = null;
+            target.ApplyTemplate();
 
             Assert.Equal(new ILogical[0], ((ILogical)target).LogicalChildren.ToList());
         }
 
+        [Fact]
+        public void Clearing_Content_Clear_Childs_Parent()
+        {
+            var target = new ContentPresenter();
+            var child = new Control();
+
+            target.Content = child;
+            target.ApplyTemplate();
+            target.Content = null;
+            target.ApplyTemplate();
+
+            Assert.Null(child.Parent);
+            Assert.Null(child.GetLogicalParent());
+        }
+
         [Fact]
         public void Changing_Content_Should_Fire_LogicalChildren_CollectionChanged()
         {

tests/Perspex.Controls.UnitTests/Utils/HotKeyManagerTests.cs

@@ -43,11 +43,13 @@ namespace Perspex.Controls.UnitTests.Utils
                 HotKeyManager.SetHotKey(button, gesture2);
                 Assert.Equal(gesture2, tl.KeyBindings[0].Gesture);
 
-                button.SetValue(Control.ParentProperty, null);
+                tl.Content = null;
+                tl.Presenter.ApplyTemplate();
 
                 Assert.Empty(tl.KeyBindings);
 
-                button.SetValue(Control.ParentProperty, tl);
+                tl.Content = button;
+                tl.Presenter.ApplyTemplate();
 
                 Assert.Equal(gesture2, tl.KeyBindings[0].Gesture);