xsetwacom --xconf outputs invalid xorg.conf syntax if asked for button mappings:
$ xsetwacom set "Wacom Intuos PT S Finger pad" Button 3 key shift
$ xsetwacom --xconf get "Wacom Intuos PT S Finger pad" Button
Option "Button" "key +Shift_L "
xorg.conf can't accept this syntax (in fact it can't specify complex actions at all), and the number of the button to be mapped isn't included.
Probably it should just refuse to output xconf syntax for button mappings, or perhaps only for simple ones that xorg.conf can specify.
Similar to [bugs:#270]; resolved by printing out an error message which suggests to use shell format "-s" instead.
Related
Bugs:
#270