Nice to know your looking at the problem. Here are my vital specs in case that helps.
Hardware: i5 2500k, 16GB RAM, 2x6950 2GB, ASUS Xonar DX Soundcard, 2 x 1080p 24" Benqs connected via DVI.
Software: Windows 7 x64 fully updated, Latest leaked AMD Cataylst drivers (same problem with the offcial 12.6) latest AMD Application profiles 12.7 CAP3.
Game Settings: Everything on max @ 1080p
I tried rwneo suggestion of alt tabbing a few times with no luck. I also tried disabling crossfire to see if that helped but it did not.
EDIT: I decided to play around with the settings some more and found that if I selected windowed mode and then hit cancel (so it switches to a window and then I dont accept the settings so it returns to full screen) my mouse is then locked to the primary screen! Sadly this only lasts till I exit the game. Its still an improvement over disabling my second screen. Perhaps this is a useful clue to you guys! Hope it helps!