I had this problem too, and like an annoying ex, I just ignored it till it stopped trying to bother me. I had this a few times, only when it was really cold in the morning. I checked the coolant, all seemed fine. When i restarted the car, I cleared itself. When I get this now, i just run the car for a min, kill the engine and then restart it. Seems to solve the problem.
It only happened a few times and when it was really cold though - so beware if it happens on a warm day with a hot engine.