Other mistake: The opening credits for season 5 show June coming out of the front door with a pitcher of what looks like iced tea, and calling for Ward, Wally and Beaver who are all working outside. But the door opens by itself as she comes out, and then closes by itself behind her. If the entire family is outside, who opened and closed the door?
Continuity mistake: After Eddie and Lumpy show up to help The Beav and Wally load the lawn trash into Lumpy's car, Eddie places a lampshade and a woman's hat over a burlap bag of trash and jokes it's Lumpy's date: "Who says Lumpy can't get a girl?" Just then the camera cuts over to Lumpy who says "ha ha ha." The street is at Lumpy's back and a car is driving in the background towards Eddie. When the camera switches back to Eddie, Lumpy approaches Eddie. The car should drive past, but it never does. (00:14:37 - 00:15:40)