When Stephen tries to talk to Shelly before her boyfriend picks her up, he was halfway up on the steps. When Brad looks at him in the rearview mirror, Stephen is already on the ground. The camera cuts back to Stephen and he is halfway up the steps.
When Shelly is talking to Stephanie in their dorm room, Shelly knocks the mirror enough to reveal a man holding a camera. This lasts for a few seconds before the mirror is restored to its previous angle.