Deliberate mistake: Rather than using real Bruce Lee footage only for the final fight scenes, so the undisguised Billy Lo's different appearance might make sense after his surgery, the filmmakers instead spliced real Bruce Lee face footage throughout the early film giving the character a constantly changing face from scene to scene.
Deliberate mistake: At Lois' penthouse, before Superman says goodbye, the image is sharp and clear. Cuts to a close-up, and then check the next wide angle where he says goodnight and flies away: It's blurry and grainy because it's not live, but a screen with a previously shot scene to allow for the camera to turn left and, in a matter of seconds, no cuts at all, show Superman magically and quickly transformed into Clark Kent.
Deliberate mistake: When the father jumps on the firemen's jumping sheet, one can see that he's very few centimetres away from safely landing on it. However, in the immediate close-up he crashes against the floor, which is more dramatic, but ludicrous nonetheless.