Comment 8 for bug 77226

I found this in the Linux-Wacom-Project ChangeLog:

2006-03-06 Ping Cheng <email address hidden>

    * Fixed a Volito bug (Kirill Frolov)
    * Fixed a xsetwacom.c typo
    * Supporting tablet attach/detach while X driver running (Christian Lupien)
    * Remove SYSCALL from xf86 calls (Christian Lupien)
    * Swapped USB tablet wheel directions (Christian Lupien)

Notice the last line... could this be the reason?