title: How to detect a drop not on the target but on the source in WPF?
body: <p>I have a UserControl in my application which is stacked in a StackPanel.
  I want to undock the UserControl from the StackPanel via Drag&amp;Drop and drop it somewhere else in my application. This works fine as long as I can intercept the DragOver, DragEnter,... events but when I drag my UserControl outside my application/window I get a "not possible" cursor.</p>
  
  <p>How do I know when I'm outside of my window and how do I know when the drop operation has been performed? I could find anything I can hook in.</p>
  
  <p>Thanks
  Martin</p>