If I turn off Cintiq 22HD, xorg hangs for about 20 seconds.
After xorg becomes responsive again, ~59MB of two error messages fill /var/log/Xorg.0.log.
[ 46.197] (EE) Wacom Cintiq 22HD Pad pad: Error reading wacom device : No such device
....
[ 67.525] (EE) Wacom Cintiq 22HD Pen eraser: Error reading wacom device : No such device
Thus, if I turn Cintiq on and off several times, /var/log/Xorg.0.log can occupy ~500MB.
While tail -f /var/log/Xorg.0.log is running, Xorg doesn't hang, but I still see those error messages. I don't know why.
I surmise Xorg hung for ~20 seconds because it had to write ~59MB of error messages at once.
dev-libs/libwacom-0.24:0
x11-drivers/xf86-input-wacom-0.34.0:0
linux kernel 4.9.16-gentoo
Fix accepted into xf86-input-wacom as commit 9126116. Expected release: xf86-input-wacom 0.36.0
xf86-input-wacom 0.36.0 released.