Audio problem: Billie says her line "he needs a new image" without moving her lips.
The New Car - S4-E6
Audio problem: When Felix and Oscar are driving around looking for a parking space, Oscar says "let's sell the car." Felix then begins talking but no audio is heard, then an overdub of him saying "Are you crazy?" which doesn't match his lips.
Kung Fu Kapers AKA Ecky-Thump - S5-E7
Audio problem: When Graham says "Struth", his lips don't move at all.
Audio problem: In the final song, "This is What It's Like to Be Lovers", the lead male studio singer starts the song, not David Cassidy, then they switch to David Cassidy's real voice halfway through for just two lines, then they switch back to the male voice of the studio singer.