In a scene towards the beginning of the film, Ben is trying to push a zombie out of the kitchen and is struggling with pushing him out the door. As the door moves, you can briefly see the reflection of a man in a white shirt who is probably a stage hand.
It wouldn't be another character reflected...
I cant remember the film excactly but weren't all the other characters except the woman in the basement still and if they weren't, no one was wearing white right?
It was definitely a member of the crew, not an actor. The reflection in the window is of a man. The only men we see up to that point of the movie was Ben who was fighting during the scene by the window, the zombie he was shoving out, Johnny- Barbara's dead brother, and Uncle Rege- the zombie Barabara was battling in the other room. We don't see Cooper or Tom until much later. It was a definite slip-up.