Alright, here's an annoying bug that not only affects the latest GA (Dec 2014), but GM running under Ubuntu 12.04, 14.04 and 14.10 as well.
The gist of it is, start GM (I've only tried 0.156 and 0.157, any game seems to do, wrally, jackal and msword does it for sure), let it run for approximately 2 hours and 25 minutes, and watch X go from about 10% CPU utilization to 100%, which causes the game to run at about 10% speed. The cards that have been tested are Radeon HD 6310 and Radeon HD 3200. Verified on two different setups. I'm not sure it's GM's fault, since it's X that eating all the cycles.
Has anyone else seen this? I'm currently testing it on GA Dec 2014 with a 9600 NVIDIA card, to see if the problem is related to the open source Radeon driver. Edit: And it's not. It does this with the nouveau driver as well.
Edit: Going into the video settings and rotating the view fixes it for (probably) another 2 hours and 25 minutes. Could it be some integer overflow or something? Segfaults after a short while.
Edit: Only 64-bit has been tested.
Edit again: The problem occurs also when non-throttled, tested with GA 2014-04-25 in VMWare, which doesn't seem to support sync to vblank?
Edit again: Also affects GA 2013-02-24 i686