mouse wheel sends incorrect buttons

[Jon Wolfgang]

I am using a Microsoft Intellimouse Explorer in xwindows on FreeBSD 
6.2-RELEASE.

The mouse works correctly (except for the side buttons - I'll worry 
about those later), but the mouse wheel has some odd behaviour in apps 
like firefox and thunderbird.  Scrolling down works correctly, but 
scrolling up seems to send a button click as well as a scroll event.

I played around with xev and found that when scrolling up, a button4 
event is (correctly) sent, but then any other action sends a button9 and 
button8 event as well.  Scrolling down only sends a button5 event which 
is correct.  Here is the relevant section in xorg.conf:

Section "InputDevice"
        Identifier  "Mouse0"
        Driver      "mouse"
        Option      "Protocol" "auto"
        #Option     "Buttons" "7"
        Option      "Buttons" "5"
        Option      "Device" "/dev/psm0"
        Option      "ZAxisMapping" "4 5"
EndSection

I added the `Option "Buttons" "5"' line hoping to remove the possibility 
of button 8 and 9 existing, but it didn't seem to work:

[jon at charon ~]$ xmodmap -pp
There are 9 pointer buttons defined.

    Physical        Button
     Button          Code
        1              1
        2              2
        3              3
        4              4
        5              5
        6              6
        7              7
        8              8
        9              9


Then I tried mapping the button 8 and 9 keys to other buttons, but 
xmodmap didn't allow it.
Also, I'm not running moused if that is significant.  Does anyone have 
any suggestions?  I have seen some similar questions on forums and the 
mailing list archives, but no definitive solutions.  Any help would be 
great.

Thanks,
Jon