The door doesn't flap, or stick right out.
The door acts like a blade/wing, the more pronounced the bubble is, the further open it will be, most of the doors I have had open up on me,just come ajar by a few inches, as the slip stream wont allow it to open too far, but also wont allow you to close it very easy either, hence slowing down and kicking in the pedal or landing if possible.
Its no big deal really, unless things start flying out.