mouse scroll up problem

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>> I have FreeBSD 6.0-RELEASE and optical Microsoft IntelliMouse 
>> Explorer, USB native, plugged to PS/2 port via it's own USB->PS/2 
>> adaptor.
>> When I scroll my mouse wheel up in X11 it acts like "scroll up + left 
>> button one/double-click". For example, in Opera, Firefox. In MS 
>> Windows mouse works correctly.
> 
> I am running the same mouse in the same way on the same release. Here is 
> what is working for me:
> 
> Section "InputDevice"
>         Identifier  "Mouse0"
>         Driver      "mouse"
>         Option      "Device" "/dev/sysmouse"
>         Option      "Protocol" "sysmouse"
>         Option      "ZAxisMapping" "4 5"
> EndSection
> 
> moused_enable="YES"             # don't use type "auto" with KVM
> moused_nondefault_enable="NO"
> moused_type="ps/2 -l 2"         # -l 2 for scroll (fails in _flags)
> moused_flags=""

I have changed settings as Pete advised. Both variants (old and new) are 
working (scrolling) but described effect remains.
Why I think that scrolling up works as "scroll + left click": for 
example, in Opera scrolling up at the top of document (when real scroll 
is impossible) result in marking the word under cursor and appearing 
context menu for very short time.