I have been trying to get my dual wheel A4 WWU-9 two wheel, 3 button mouse to work on Slackware 10.1 with 2.4.30 kernel and xorg 6.8.2.
I use IMPS/2 driver or ExplorerPS/2 protocols and both wheels have vertical scroll action.
xev shows that BOTH wheels are seen as buttons 4 and 5, so no wonder xorg gets confused.
I found a link to a patch to mousedev.c for A4 for an old kernel (2.4.20).
Has this gone into 2.6.x?
http://home.bawue.de/~rguent/4D-Maus/