Wheel mouse oddity - wheel only reporting button release

[Jukka A. Ukkonen]

Hi,

Does anyone have any idea what is going on when a ps/2
mouse with a wheel (actually a trackball) sometimes works
just fine and sometimes the wheel reports button release
events only?
This is happening on an AMD64 system running FreeBSD-9.0.

I used truss to trace moused to see how the basic
3 buttons always send "\t\0\0", "\n\0\0", or "\f\0\0" for
button press and then "\b\0\0" for button release.
The wheel only sends "\b\0\0" for button release.

This looks awful lot like moused failed to talk to the
device using level 1 or level 2 protocol, decided to fall
back to level 0 protocol, and silently went on using
3 byte packets which cannot carry the data for more
than 3 buttons.
If this is the case and level 1 was explicitly requested,
I would expect moused to complain loudly about not
being able to use the requested protocol level.

Has anyone else seen something similar?
Can this behavior be changed using hint.psm.0.flags
in /boot/device.hints?
Could this be a side effect of a KVM switch getting
confused and forcing the protocol to downgrade to
level 0?
Should I simply replace the KVM switch?

--jau