When Buffy, Xander, and Willow go to check if any members of the swim team were injured, they go to the computer lab. The establishing shot for this is the gang sitting in the background talking while at the main desk, while the camera is panning across a computer monitor in the back of the class, there is what appears to be a black rectangle moving across the monitor. It is incredibly obvious that this is the reflection of the camera on the glass.
When in the Mustang, Cameron locks the door to keep Buffy from escaping. Opening those doors from the inside automatically unlocks them.