title: How to fix WPF render exception on floating panel resize?
body: <p>EDIT: This happens because the dockable panel is semi-transparent when it's moved to floating. The fix was to disable transparency. </p>
  
  <p>I use a custom panel-feature (3rd party, non-public NuGet) that has visual-studio like dockable panels. If I float a panel and resize it (couple of times) on Citrix XenApp it crashes. With following stack in log file (only few lines).</p>
  
  <pre><code>Unhandled exception. System.Runtime.InteropServices.COMException (0x88980406): UCEERR_RENDERTHREADFAILURE (Exception from HRESULT: 0x88980406)
  
     at System.Windows.Media.Composition.DUCE.Channel.SyncFlush()
  
     at System.Windows.Media.MediaContext.CompleteRender()
  
     at System.Windows.Interop.HwndTarget.OnResize()
  
     at System.Windows.Interop.HwndTarget.HandleMessage(WindowMessage msg, IntPtr wparam, IntPtr lparam)
  
     at System.Windows.Interop.HwndSource.HwndTargetFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean&amp; handled)
  
     at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean&amp; handled)
  
     at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
  
     at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
  </code></pre>
  
  <p>It does not happen when I run it in any environment except Citrix. And it can be reproduced in all customer environments with same Citrix version. This was not reproducable with older version of Citrix XenApp but it's not possible to ask customers to downgrade.</p>
  
  <p>This happens with Citrix version 7.6 on 2012 R2. Seems to happen on all 7.6 and one 7.9 installations.</p>
  
  <p>Does not happen on 6.5 on 2008 R2.</p>