Comment # 12 on bug 79850 from Michel Dänzer

I noticed artifacts as you're describing in armagetronad. It's actually
DRI2CanFlip() which failed, because the window pixmap is not the screen pixmap.
This turned out to be because SDL 1.2 enables backing store when supported:
https://bugzilla.libsdl.org/show_bug.cgi?id=2602

Even if awesomenauts doesn't use SDL 1.2, it might be worth disabling backing
store via

 Option "BackingStore" "off"

in xorg.conf or the -bs Xorg command line switch.