Fix Unit Tests & Value Restore on .NET Properties

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Xaml/XamlModelProperty.cs

@@ -133,6 +133,11 @@ namespace ICSharpCode.WpfDesign.Designer.Xaml
 			}
 		}
 
+		internal void SetValueOnInstance(object value)
+		{
+			_property.ValueOnInstance = value;
+		}
+
 		// There may be multiple XamlModelProperty instances for the same property,
 		// so this class may not have any mutable fields / events - instead,
 		// we forward all event handlers to the XamlProperty.
@@ -197,11 +202,6 @@ namespace ICSharpCode.WpfDesign.Designer.Xaml
 		}
 				
 		public override void SetValue(object value)
-		{
-			SetValue(value, false);
-		}
-		
-		private void SetValue(object value, bool withoutUndo)
 		{
 			XamlPropertyValue newValue;
 			if (value == null) {
@@ -223,7 +223,7 @@ namespace ICSharpCode.WpfDesign.Designer.Xaml
 			}
 			
 			UndoService undoService = _designItem.Services.GetService<UndoService>();
-			if (undoService != null && !withoutUndo)
+			if (undoService != null)
 				undoService.Execute(new PropertyChangeAction(this, newValue, true));
 			else
 				SetValueInternal(newValue);
@@ -308,11 +308,14 @@ namespace ICSharpCode.WpfDesign.Designer.Xaml
 					}
 				}
 				else {
-					try {
+					if (property.DependencyProperty == null) {
-							property.SetValue(oldValueOnInstance, true);
+						try
+						{							
+							property.SetValueOnInstance(oldValueOnInstance);
 						}
 						catch(Exception)
 						{ }
+					}
 
 					property.ResetInternal();
 				}