title: OverlayLayout doesn't respect the overlay order with focus change
body: <p>I encountered a problem with <code>OverlayLayout</code>.</p>
  
  <p>Basically, I created a component which allows to unroll an overlay content above a main content (like a drop down menu). It works!</p>
  
  <p>The problem is: if I put a <code>JButton</code> on the main content (the content below), when I click on this button, then the button starts to appear above the overlay content !
  I don't know why?</p>
  
  <p>Does anyone know what the problem is ? Is it maybe the focus ?</p>