The daytime close-up of the entrance to Sheldon's dorm, Bower Hall, is completely different than the nighttime entrance in the long shot of the whole building.
When Mary and George enter the bedroom Mary tells George to shut the door 'just in case' anyone shows up which he does. A minute later she is angry and storms off out of the room by opening the door without unlocking it. As the door was locked, it would of been impossible for her to do that without unlocking it.