On my intel card, GL apps in fullscreen just show a black screen with current git or 18.104.22.1681. Works with 2.7.1.
I'll try to bisect this one.
Created attachment 27572 [details]
xorg log with the problem happening
Created attachment 27573 [details]
reg_dumper with git-code / bug appears
Created attachment 27574 [details]
reg_dumper with 2.7.1 / works fine
bisecting failed, I stepped over compile problems with inbetween versions. I attached reg_dumper output with a fullscreen app and a log with debugging. Hope this helps.
Maybe this is because 2.7.1 uses EXA by default and 2.7.99.x uses UXA by default. How about if you set AccelMethod UXA in xorg.conf with 2.7.1?
What's the mesa version? Can you try mesa 7.5?
This got fixed somewhere between 22.214.171.1242 and 2.8.0.