Visible crew/equipment: In season 2, episode 6, "Have You Met Miss Dietz?", at 0:07:45 into the episode, the camera is on Carol sitting at her desk talking. Behind her, you see a shadow of someone walking by. (My guess is that it was Jerry Robinson getting into position to enter the scene about 23 seconds later from that same location.)
Continuity mistake: In the opening credits where Bob is on the 'el' platform, the train car he is sitting in is different from the one he enters in the scene before. The car he is shown entering is an older car with small windows and the car he is sitting in is a newer model with much larger windows.
Continuity mistake: "Let's Get Away From It Almost": About 2/3 into the episode, Bob pulls out his suitcase to start packing, sets it on the bed and opens it. After being interrupted by their neighbor the scene moves back to the bed where the suitcase is closed again even though no one has gone near it.