Yeah, I've had that happen when I pressed my auto-follow hotkey while I was holding another key down. There are also times when I did not have the group on auto-follow, just had them standing in a spot, and pressing an assist macro while holding another key down would also cause them to suddenly start auto-running. And it sure was hard to get them to stop. :P

Just one of the many little quirks that I've had to learn to watch out for as I learn to multibox. At least I no longer switch between button pages on the alts. >.<