The Cook, the Steve, the Gayle, & Her Lover - S6-E6
Continuity mistake: In this episode, the whole family is surprised that Gayle is dating Mr. Frond. But in S6-E4, they know Gayle is dating Mr. Frond because Gayle is upset he went to his aunt's for Thanksgiving.
Suggested correction: That's because the episodes were aired out of order. This episode (production code 5ASA12) was produced before "Gayle Makin' Bob Sled" (production code 5ASA17). It's not a mistake for the show. The network decided to air the Halloween, Thanksgiving, and Christmas episodes first so they could air before the respective holidays.
Other mistake: When Tina is writing in her diary and we hear the voice-over she says "So, it's a really great bang for your buck-ing bronco" but when we see the diary it reads "So it's really bang for your buck-ing bronco."
Continuity mistake: Part of the plot of the episode is the port-a-potties being in front of Bob's restaurant. But on the day of the parade, there's a shot of The Land Ship going down the street and there are no port-a-potties in front of the restaurant. When Jimmy comes over to make fun of Bob, they're back in front of the restaurant.