Comment 2 for bug 1381638

I managed to find the reason for the buttons not working: the Wacom option 'tabletpcbutton', which used to be 'off', is now 'on' by default. This can be changed manually e.g. with 'xsetwacom', but is reset to 'on' after reboot.
I think it would be better if the default was still 'off' as it used to be, otherwise the buttons only work when the stylus is touching the screen and not when hovering, which is less useful and unexpected behavior when upgrading from a previous version.