That 'fix' for the grey rect. issue smells distinctly like yet another swing hack fix
Why do you think so?
I can't see what's wrong with using something which is already stored in an image and repaint it again instead of clearing the image, runing a lot of code to draw the same stuff into the image again and blit that.
In fact this is also the way Windows (well at least till XP) handled its drawing, and Windows its known to perform quite well when it comes to perceived performance of common-controls-based desktop apps.