I've had this happen about 3 times in the last 1.5 years (once when merging onto the highway....a little scary that time - this was the day after the car went in for the ECU update). It hasn't come back recently, though, so I can't shed any light on this. Sorry.
These cars really do depreciate, don't they? I tried to trade on a GTI last Summer, but wasn't willing to take the $6.5k drop, so I'm going to keep it until the Mk7 Golf comes out. If you're dying to get rid of your car, you could minimize the drop by selling privately.