Revealing mistake: When the robot releases the balloon with the bomb attached, the wires used to pull the balloon up are visible as the balloon rises through the skylight.
Adventures of Superman (1952)
1 revealing mistake in season 6 - chronological order
Starring: George Reeves, Bill Kennedy, Jack Larson, John Hamilton
Revealing mistake: When the robot releases the balloon with the bomb attached, the wires used to pull the balloon up are visible as the balloon rises through the skylight.
Lois Lane: Eureka.