> I tried that several times; about half the time it worked just fine,
> the other half I got the slow redrawing.  Once I got an error while
> trying to draw the main pane of the debugger.

Have you checked whether your image was in a bad state already? The 
above would not *create* such a problematic state but it would suffer 
from it if your image were already in that state.

Cheers,
   - Andreas