Was the oxygen mask, on this flight, out of order? Recently I was on flight where the panel for the oxygen mask, above my seat, looked like on the picture: the "button" in the middle of the panel was extended, turned and was showing a red tag on the side.

I asked a member of the cabin crew if this indicated a problem and the response - after he had tried to turn and push it in - was "I don't know, I don't think so". The fact that he couldn't turn it, or push it back into the panel, makes me think that it is more than just a locking mechanism, that it might have indicated that the system was out of order and I should've moved to a different seat.

Was my hunch correct, does this indicate a faulty oxygen mask?

The plane was an Embraer 190.
According to this Airbus training manual, pages 10 and 11, that's the test door stop.

As you can see in the video you added, resetting the masks is a pain, so the little red stop is there to catch the door and stop it from fully opening.


  Manually operated doors stops are fitted on the container doors to allow an operational test of the mask release system.
  When set to test position the door stops will prevent doors from fully opening and masks from dropping out of the Container.