https://bugs.freedesktop.org/show_bug.cgi?id=75357
--- Comment #7 from Michel Dänzer michel@daenzer.net --- When you try switching VTs after the problem occurs, do lines like
(II) AIGLX: Suspending AIGLX clients for VT switch (II) AIGLX: Resuming AIGLX clients after VT switch
appear in the Xorg log file? It sounds like maybe there's just a problem lighting up the monitor again after it's turned off...