https://bugs.freedesktop.org/show_bug.cgi?id=108095
--- Comment #5 from Michel Dänzer michel@daenzer.net --- Does restarting xfwm4 with any of these arguments make a difference?
xfwm4 --replace --vblank=off xfwm4 --replace --vblank=glx xfwm4 --replace --vblank=xpresent