Windows will detect a Serial GPS device attached to a Com Port as a Serial Mouse and cause some "crazy" behavior. Typically it will continually move the mouse to the top right corner of the screen every 1 second (the update interval of the GPS unit)
My particular application is a GPS unit plugged into a Toughbook CF-31 Docking station.
To resolve the problem, we can simply tell Windows not to enumerate any "Plug and Play" devices on the serial port.... or what it thinks are plug and play devices.