This happens to me as well, but I'm on a GTX 570. I get around it by clicking the minimize button on the Start Screen. If I do this, the window will do a sort of refresh (without actually minimizing) and everything will become normal again. I just have to remember to do it every time I exit a flight and everything is OK. Of course I'd like to fix it if possible, but as is I can live with it. Hopefully you experience something similar.