The door was already open

You know that scene in the library right after Sara tracked her dead mother to the elevator? She tried to open the glass door to go back into the library, but they were locked. She got scared or something and they mysteriously opened up. Except if you look to the right, that door is already open. I guess the director just didn't want people to notice and used that open passage to get the steady cam to be able to track Sara into the library.