title: Transparent control not capturing mouse events
body: <p>I have a window with a transparent background (not <code>null</code>). Inside that window, I have a user control, also with a transparent background.</p>
  
  <p>The window receives mouse events, but the user control does not. </p>
  
  <p>If I change the background of the user control from <code>Transparent</code> to <code>#01000000</code>, then the user control starts to receive mouse events. However, controls hosted within the user control (which are themselves visible) never receive mouse events, regardless of the user control's background.</p>
  
  <p>Any ideas?</p>