It's a known issue with Catalyst 11.5, though the only major game fix I'm aware of in 11.5 Hotfix over 11.2 is tweaks for Brink... which did not necessarily work for some users. All other updates in the sequence have been small performance optimizations and a few other things mostly related to very specific usage scenarios.

Running the game full screen does seem to lower the instance of these events, but if 11.2 is not an option then you're stuck waiting to see if the 11.6 release is better.

I would recommend using the Driver Feedback Form to let them know they've got a problem. The more users that report it the more likely they are to fix it. (Only took a month to fix the flashing light surfaces they introduced in 11.3...)

Edit: Sniped! That's what I get for taking the time to pour over some release notes. :/

Really? I was not expecting that out of the 11.5b hotfix, though part of the reason it arrived was unsatisfied users with Brink (another OpenGL game). So I guess it makes sense that a few fixes snuck in. Please update us you observations later and I'll see if the same follows on my Radeon 6950.

OzNeverSleep
When installing an older driver in place of a new one you must first uninstall the current driver. The install manager included in the Catalyst download will not do this for you.

For the record, the 11.5b Hotfix seems to be working quite well on my system. I'm gonna give it a whirl on a different computer with the same problem later.

welp, same issue with 11.6. running fullscreen seems to solve the issue. knew i shoulda stayed with 11.4