I had something similar but even more strange: The receiver was directly exposed to bright sunlight. I could see its LED flashing very often and sometimes a command was understood..
now that you point me to the mouse, i think that my problem has appeared when i have installed a new wireless kb/mouse. Since i upgraded mp at the same time, i thought it was a new svn bug ...
i don't want to unplug the mouse or replace it, and i never use the wheel inside mp. is there a way to tell mp not to use wheel ? or even better, is there a way to desactivate big jumps with the wheel ?