I've caught it doing this several times, even after I held the button down to turn off the automatic mode.

 

Note that you can't recirculate unless you are using the AC. If AC is off, then it will vent outside air by default. Also, I'm not sure about this, but I think there are some settings (like defog/defrost) that will force it to change to outside air.

 

Oh the AC is on.