In one episode, the Cunninghams are on their way to the movies. When Ralph asks them what they are going to see Joanie tells him they are going to see Psycho. However, the episode is set in 1957, three years before the film premiered.
The changing of the interior of the house after the second season messed up the scheme of the house. From exterior shots the driveway/garage of the Cunningham house was to the right of the front door, while from the interior sets the garage was still to the right of the front door (i.e. it would be on the left as viewed from outside).
The restrooms at Arnold's restaurant have the Men's room on the left, and the Ladies' room on the right. But, in all of the shots of the guys coming into the restroom, they walk in making an immediate right.