I have recently encountered this bug as well but my solution was suprisingly....unusual. By default Ive always used catalysts "use application preference" setting for Anti-aliasing. I tried the force fix that others suggested. Didnt work.....however..by setting the AA to "over-ride application settings" and setting it to max 16x .....it worked perfectly. Three of my friends had the same issue. Worked the same for them. For reasons I cant fathom, the games built in or lack of AA was messing with the ATI cards.