I have a strange problem with ATI cards on Ubuntu 12.04 LTS and 13.10.

It appears that when the framerate gets above about 80, the screen actually stops refreshing...so while the FPS reading remains high, the screen appears to be quite laggy, with pauses of half a second or so. Has anyone experience anything like this?

I also noticed that if I simply call glXSwapBuffers(), without attempting to mess with vsync at all, the default behavior seems to be to have vsync turned off. I would have expected vsync to be enabled, unless I specified otherwise.