Mr. Walsh Goes to Washington (2) - S4-E32
Audio problem: During the scene where David and Babyface are talking and Babyface asks David to fill in as one of the keyboardists for his carnival show, the camera shots going back and forth from both behind David and Babyface show them speaking, but it is very clear their words don't match their lip movements.
Other mistake: When the show aired in 1990, in the pilot episode Brenda falls for Jason. She later on reveals herself to be a "16 year old junior" in high school. Season 2 opens up with the gang on summer break which technically would make them going into their senior year. It wasn't until Season 3 that they were going into their senior year. They graduated in 1993 from West Beverly but the show debuted in 1990 so technically they should have been sophomores.
Emily Valentine: This isn't Beverly Hills! It's Knot's Landing.
Trivia: When Brandon and Kelly leave the movie theater, they pass a billboard for The House of Yes, which co-starred Tori Spelling.
Question: Was Valerie Malone introduced this season to balance out Brenda's departure?
Chosen answer: Yes, she was.