Bug#607242: syslog shows messages from psmouse.c
For my part I'm certain of it: this is a failing mouse overloading
some part of the link. The mouse now misbehaves rarely but it's
plainly my middle mouse button sizzling briefly and everything
recovers fine, no desyncs or parity errors at all after I backed off
further to rate=40.
shirish, if you'd rather not have your mouse driver unloaded however
briefly you can do
$ sudo sh
# echo 40 >/sys/module/psmouse/parameters/rate
and see if it doesn't do the same for you. If it works, don't forget
to stick "options psmouse rate=40"" in /etc/modprobe.d/psmouse.conf
so it gets restored on reboot. If you'd like to see for yourself what
that file does, do "man 5 modprobe.conf` at any shell prompt.
Merry Christmas, Happy New Year, all that good stuff. :-)