https://bugs.freedesktop.org/show_bug.cgi?id=84944
--- Comment #28 from Michel Dänzer michel@daenzer.net --- (In reply to warpme from comment #27)
[2654838.916] Can't flip because can_exchange failed
Oops, my first debugging patch has a bug which causes can_exchange to spuriously return FALSE. Does it work if you remove that patch?