Created Unassigned: AvalonDock InvalidOperationException calling TransformToAncestor [21617]

Hi all,

I'm using AvalonDock 2.3 in simple WPF project as follows:

```
<Window x:Class="AvalonTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:xcad="http://schemas.xceed.com/wpf/xaml/avalondock"
Title="MainWindow" Height="350" Width="525">
<Grid>
<xcad:DockingManager>
<xcad:LayoutRoot>
<xcad:LayoutPanel>
<xcad:LayoutAnchorablePane>
<xcad:LayoutAnchorable>
<Button Content="Test" Click="ButtonBase_OnClick" />
</xcad:LayoutAnchorable>
</xcad:LayoutAnchorablePane>
</xcad:LayoutPanel>
</xcad:LayoutRoot>
</xcad:DockingManager>
</Grid>
</Window>
```

Code behind:
```
private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
var button = sender as Button;
var transform = button.TransformToAncestor(this);
}
```

Clicking the button works as expected as long as the LayoutPanel is docked. When undocked, clicking the button leads to an InvalidOperationException:

> The specified Visual is not an ancestor of this Visual.
bei System.Windows.Media.Visual.TrySimpleTransformToAncestor(Visual ancestor, Boolean inverse, GeneralTransform& generalTransform, Matrix& simpleTransform)
bei System.Windows.Media.Visual.TransformToAncestor(Visual ancestor)
bei AvalonTest.MainWindow.ButtonBase_OnClick(Object sender, RoutedEventArgs e) in AvalonTest\MainWindow.xaml.cs:Zeile 37.
bei System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
bei System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bei System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
bei System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
bei System.Windows.Controls.Primitives.ButtonBase.OnClick()
bei System.Windows.Controls.Button.OnClick()
bei System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
bei System.Windows.UIElement.OnMouseLeftButtonUpThunk(Object sender, MouseButtonEventArgs e)
bei System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
bei System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
bei System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
bei System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bei System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
bei System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e)
bei System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
bei System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
bei System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
bei System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bei System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
bei System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
bei System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
bei System.Windows.Input.InputManager.ProcessStagingArea()
bei System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
bei System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
bei System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
bei System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
bei System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
bei MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
bei MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
bei System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
bei MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
bei System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
bei MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
bei MS.Win32.UnsafeNativeMethods.CallWindowProc(IntPtr wndProc, IntPtr hWnd, Int32 msg, IntPtr wParam, IntPtr lParam)
bei MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
bei MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
bei System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
bei System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
bei System.Windows.Threading.Dispatcher.Run()
bei System.Windows.Application.RunDispatcher(Object ignore)
bei System.Windows.Application.RunInternal(Window window)
bei System.Windows.Application.Run(Window window)
bei System.Windows.Application.Run()
bei AvalonTest.App.Main() in AvalonTest\obj\Debug\App.g.cs:Zeile 0.
bei System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
bei System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
bei Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
bei System.Threading.ThreadHelper.ThreadStart_Context(Object state)
bei System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
bei System.Threading.ThreadHelper.ThreadStart()


I've attached the project as well.

Cheers
Nirraven