Visible crew/equipment: When Mr. Purzan finds out that Stephanie doesn't want to date him and runs off like a little nancy-boy, we see his reflection pass through the picture in the hall. A moment later we can see the reflection of two people pass in the opposite direction but no one walks back into the room.
Other mistake: When playing poker, Stef says she has all hearts which is a flush. However if you look at the cards she puts on the table, there is a 6 of diamonds and 3 of clubs. Therefore, not a flush. Everyone at the table, (Lou, Mr. Prezants, Deacon, Spencer and Doug) all agree it's a flush.