De-glitching overlapping windows
<p>If I create multiple overlapping windows (ie; like on a real computer's desktop) the redisplay is very glitchy.  Each window paints back-to-front,
resulting in the right final picture but with lots of unpleasant intermediate
states.</p>

<p>Is this an artifact of the simulator environment, or does it reflect
the reality of the target platforms?</p>