That's because the outside vent is still open. The wind pressure forces air through the system as long as the outside vent dampers are open. If you push the recirculation button it will close the outside vent dampers. I am not sure of the logic behind it, but it was that way in my Gen 1 X as well.
Not sure if this is still true, Bet it is though...but around 1972 or so it was a mandated safety feature that cars had positive air flow at all times so as to clean the cabin of possible carbon monoxide exhaust gases. Manufacturers accomplished this by spinning the fan a bit even when in off as long as the key is on. This is what the vents are in the back for, it allows the air to escape. Fresh air in dirty air out. It don't help when you pass a Skunk sleeping on the side of the road though huh? MC
Yes I know he is right for sure. And I know I am right also it's just I don't want to look up the info to prove it. But if the vent is open, you will get flow relative to your speed. However even if you are stopped, they Positive Ventilation takes over and the fan will still keep fresh air flowing at a hardly noticeable rate. The Fan gets no rest! MC
If you take it apart and look, you will see that when you completely close the door as far as no recirculate,,, that door normally electrically or vacuum operated will not close all the way as in ....impossible. So, when you shut it all down and turn it all off, you still have a spinning fan and fresh air even if a minimal amount. It's a requirement/safety feature same as seat belts, vents on gas tanks, bumpers, crap like that.