The airlock door can close on top of a dupe if they stop to interact with something while in the door way. Dupe stops in doorway; door closes after the appropriate delay with dupe still standing there as if nothing's happening. It didn't affect the dupe in any way, but it was certainly odd-looking. There was a second dupe going through the door at the same time in case that might be what triggered it.
Have a dupe attempt to interact with a tile that's just in range when they stand in the doorway.