Disabling the Overlay doesn't help my friend.
Also removing the config-folder and backtracing with gdb didn't the job for him. (His backtrace was exactly the same: in [Linux] Game crash when shootingComment by LuckiFebruary 2014
I can say, that Gnome 3 cause this problem.
I have the same problem in L4D2 ans NS2 - Killing Floor runs without this problem.
And I have only with these two games this problem.
I've tried to backtrace the problem with gdb, but with gdb everything works fine.
After closing gdb and NS2 and starting NS2 again, it works without gdb.