It appears that there may be a compatibility issue between some iterations of Apple mice and certain portable models. MacFixIt reader J. Strauss writes "I have an iBook 12" dual USB, and a Titanium ...

Rosemary Brown describes a problem noted by a few other MacFixIt readers, where a UPS (uninterruptable power supply) seems to "hog" the chain, and produce strange problems for the keyboard and mouse. ...