Drawing gets cleared on opening of context Menu in Windows7

Question

Hi,
 I am working on a drawing application like paint. It is working very nicely on winXP, but on testing on windows7 it is giving some problem.
1. On Opening of context-menu, the drawing that user have drawn automatically gets cleared.
2. I have added one form as child form of other form and drawing on main form. While moving this child form over drawing drawn by user, that form work as eraser which erases all drawing.

I am not getting any workaround without switching off auro. But i don't want to do that.
Anyone have any clue or any workaround for this issue?

It is urgent.

Thanks,
SD