I also get this from time to time, but the interesting thing is, it only happens in WoW. I can play other games for hours and not experienced any "mouse freak" but as soon as I play WoW it inevitably happens. Sometimes it might happen three or four times a minute other times it might be fine for hours. I've tried various mouse mats, cleaning the mouse obsessively and even resorting to swearing. It's not limited to one mouse either, I've used to mice and experienced the same erratic behaviour from time to time.