https://bugs.freedesktop.org/show_bug.cgi?id=100289
--- Comment #13 from OmegaPhil@startmail.com --- Right, have just had my first example of the failure without TearFree and with no associated warning in Xorg.0.log - I'm going to see if I can poke at the problem from the XFCE4 side (I want to demonstrate a program being told to change the monitor layout at the very least, then go backwards from there).