title: wpf contextmenu submenu placement
body: <p>What determines the placement of submenus in a contextmenu?</p>
  
  <p>I create a ContextMenu dynamically and set the PlacementRectangle so that it appears in the center of the screen - so far so good.</p>
  
  <p>Some of the items show a submenu.
  However the submenu always defaults to showing on the left.
  It should default to showing on the right of the parent item selected.</p>
  
  <p>How do I change this?</p>