Some areas of the window are not redrawn and consequently useless areas remain on screen without deleting.
that might be your graphics card driver bug.
my buddy has the same problem, while i don't.
update your drivers and then try again
I had something like that while using C2 on my laptop too.
You should try to "reset dialogs" in the preferences, that fixed the problem on my end.
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I have updated drivers.
For my tests, this does not happen with a Aero theme selected.
This happens if you have a custom theme on saving resources, non-transparent windows etc ...