Other mistake: Towards the end when Janet, Brad, Oliver and Betty are singing "We're going to do it anyhow," as they are dancing down the aisle, Betty very visibly trips and grabs Oliver to stop from falling over.
Other mistake: During the 'Little Black Dress' number, look carefully at Cosmo's plans for the dress, they read 'The Brad and Janet Show' as this was to be the original title of the film. It doesn't really fit for Shock Treatment because the show being planned is only Janet, Brad is locked in a cage.