Don't use Nitrous. Revert back to DirectX. Nitrous is nothing but a headache in 2012.
Jens, it sounds like you need to set Max to properly refresh your windows. It's under your configure your display driver in Max. Set it to redraw on windows expose. Or it's an issue with your computer's display card. Easy solution, don't switch windows while in Max. Also, make sure you are not in Nitrous. That may not play well with a Mac.