title: Why does a WPF Popup close when its background area is clicked?
body: <p>I have a WPF <code>Popup</code> control that contains some editing controls (list boxes, text boxes, check boxes) laid out with quite a bit of whitespace.</p>
  
  <p><code>Popup.StaysOpen</code> is set to <code>False</code>, which is required.  If the user clicks elsewhere in the application, the editing operation should be considered aborted and the popup should close.</p>
  
  <p>Unfortunately the popup also closes whenever the user clicks within the background region of the popup (the space between the edit controls).</p>
  
  <p>I've tried setting the popup to be <code>Focusable</code>.  I've also tried setting the popup's child (a <code>Border</code>) to be focusable.  No luck on either front.</p>
  
  <p>Furthermore, the mouse event seems to tunnel through the popup.  Whatever element is underneath the popup when I click it becomes focused.  This is despite both the <code>Popup</code> and the <code>Border</code> (into which I'm clicking) having both <code>IsHitTestVisible</code> and <code>Focusable</code> set to <code>true</code>.</p>