libXtst's XTestFakeDeviceKeyEvent() isn't useful
Submitted by Bastien Nocera
Assigned to Xorg Project Team
It unfortunately doesn't work as well as XTestFakeKeyEvent() for most uses, as modifiers aren't latched, and it seems that key press and key releases need to happen together to work adequately.
All this seems to be because XKB doesn't apply the xtest mappings: /usr/share/X11/xkb/compat/xtest when emitting the key press/releases on behalf of another device.