Monster in the Playhouse - S1-E9
Revealing mistake: As Reba the Mail Person exits the Playhouse, she goes past the window, and you can see her exit the sound stage through a door painted the same as the background.
Pee-wee's Playhouse (1986)
Episode list - season 4
Starring: Paul Reubens, William Marshall, Alison Mork, George McGrath, Ric Heitzman
More mistakes in Pee-wee's Playhouse
Jambi: Mekka Lekka Hi-Mekka Hiney Ho.