Is this just a 'quirk' of ownership?
Absolutely not. This would be a first I've ever heard of this glitch.
I cannot imagine it being a result of the A/C - the windows steaming up would be indicative of the warm air mixing with the moisture from the A/C once the vent pump was turned off; however, actual steam would seem to indicate a fluid leak onto something hot - as Cereal states, onto the manifold, etc.
If the car has been parked outside, could it be attributed to water that has frozen and them thawed as you drove the car?
