Other mistake: When Jimmy leads Dave to the elevator, the door opens as they are headed to it, but no one gets off, and no one hit the button to call the elevator.
Who's the Boss: Part 2 - S4-E13
Other mistake: Robert Hegye's character in the show is called Sal but is credited as Al.
Who's the Boss: Part 1 - S4-E12
Other mistake: The whole time Beth is typing the computer screen never changes, it actually looks to be some sort of start screen.
The Secret of Management - S4-E9
Other mistake: The coffee mug that Cadbury gives Bill is empty.