I have an interesting question. Some older elevators (usually made by Otis or Westinghouse if in the United States) have buttons that latch in when pressed, and when the elevator gets to the floor, the button pops out (hence me calling them pop-out buttons, though that might not be what they are actually called). Does anyone know what the purpose of this was, instead of using normal buttons? You could also pull out the buttons to cancel car calls, was this an intentional feature?

Call latching. The call holding relay was the button.

Little more here,

There was a large rectangular behind the push buttons. When last call was answered polarity was switched on the magnet to reset them. Expensive deal, now-a-days. These magnets might as well be made of platinum.