*Different operating system (Windows / Linux)
*Different behavior (borked graphics / crash)
*Different game (Quake Live / Savage 2)
It's probably yet another regression in the massive changes made to the OpenGL code as of Catalyst 10.5. When they extended their OpenGL implementation to support GL 4.0 and GLSL 4.0, they inadvertently created a large number of regressions in their OpenGL implementation that still stand today. Just because you're having an issue with the same release of Catalyst is no reason to believe it's the same exact code causing the breakage. My hypothesis is that the evidence suggests there is a different breakage. And knowing ATI, it is extremely plausible that there are even more new OpenGL problems since 10.5 than either you or I am experiencing. It'll be 2011 before these hit a stable release, I'm afraid.