Express buttons instantly being released
As of now, every key input besides the built in 4 builtin keys (ctrl,alt,meta,shift) are seen by xsetwacom as +key -key, so you are unable to hold them down.
Suggestion: either add a toggle that would let you toggle keys between the current [+key -key] and [+key], or add an option to globally make every key be seen by xsetwacom as +key