Elevators sometimes have an anti-mischief feature where they will deselect every floor if all the floors are selected in a brief period of time. The cab will slow to a stop if no new buttons are pressed. It’s kind of eerie, actually.
The elevators at my office were upgraded a few years ago and one of the elevator techs happened to mention it to me. I tried it out while alone, for obvious reasons.
Cool. I was hoping for something other than "I exhaustively test all new elevators".