Calling "Window.PointToScreen()" from an event handler that is called while the Window is closing (eg. "Window.MouseLeave") "throws" a Win32Exception on a 64-bit Windows system. The problem there is that somehow the call stack gets screwed so that this exception can't even be caught. Note that this is no problem on 32-bit Windows system; here an InvalidOperationException will be thrown and the call stack remains intact.
For more information, see here: http://manski.net/2011/06/27/wpf-crashes-on-exit/