I was in the metro today and the train arrived at the stop as usual, but as it came to a complete stop the doors didn't open. The conductor was obviously trying repeatedly to open the doors because the red lights at the top of the cars kept flickering on and off (they usually stay on when the metro doors are open).
After about 2 minutes trying to get the doors open, the conductor shut down the metro train, so the air vents stopped and lights when out for a brief moment as she/he restarted the engines. It's perfectly logical that this is possible as after all, they have got to start the trains at the beginning of the day to get them moving along the metro lines but it was just bizarre to see a train in its powered down state.
The good news is whatever restarting the engines does fixed the problem - the doors opened immediately after the conductor "reset" the metro train.