I am running Xubuntu 14.04 and my tablet is CTH-680 or Intuos Pen and Touch Medium.
I used xsetwacom to assign key press a, b, c, d to buttons 1 to 4 of "Wacom Intuos PT M Finger pad" but when I assigned the fourth button, xsetwacom showed me
Unsupported offset into 'Wacom Button Actions' property.
When I tried to test the express keys only thebuttons which were assigned to the buttons to the left of the tablet worked. The buttons at the right were still the same(forward and back).
When I tried the other devices, the buttons that change are the pen's.
I am still new to Linux, so it would be appreciated if the answer would be easy to understand.