Continuity mistake: When evil Superman crushes Clark's glasses, they swap around 180ยบ between shots.
Revealing mistake: When Vera is reading the Time magazine, it's missing the date and price on top of the letters, revealing it's a fake cover.
Continuity mistake: From the wide shots, the black stripe on the side of the oil tanker is 12 to 15 meters wide, but on the close-up of evil Superman destroying the tanker shows it's thinned to barely a couple meters wide.
Visible crew/equipment: When bad Superman is bending the glass from the bar, watch the right side of the screen and you'll see the reflection of the cameraman slowly sneaking in.
Visible crew/equipment: When Brad opens the door to Gus, cameras and equipment are reflected in the glass.
Factual error: The supercomputer has the British spelling 'Defence' written on it, instead of the American 'Defense', even though the movie takes place in the USA.
Visible crew/equipment: When Superman is landing to stop the plough machine, the wires holding him are visible.
Revealing mistake: When Evil Superman blows out the acid from his hands, the tube used to throw the liquid can be seen for a brief second standing out from his finger (hard to notice but it is there).
Continuity mistake: Before Gus gets on the skis his shoes are grey with thick black stripes. When he lands he has plain brown shoes.
Continuity mistake: After Superman is swallowed by the super computer, red acid spills on the computer. Right before the acid breaks the floor, the computer is shown again, completely clean.
Revealing mistake: Evil Superman supposedly holds Clark by the back of his shirt, but what we really see is his hand behind the back and not holding anything, or at most a part of a dummy which was superimposed with Christopher Reeve.
Continuity mistake: When the Olympic marathon runner holds the torch while running on the track toward the stairs, he has a large upper body build. Also, his shirt has a very noticeable logo that is lying right on his sternum. As he climbs the stairs we see him from behind and this is the last of the real footage from the Olympics. The actor holding the torch, that gets blown out, does not climb the stairs near as gracefully as the Olympic athlete. When they show him from the front, not only does he have very little upper body muscle, but his face is nowhere near the same as the athlete in the stock footage. (01:12:10)
Continuity mistake: When Ross is bitten by Gus, his hand lies vertically on Gus' head. A shot later it lies horizontally. (01:41:29)
Continuity mistake: The shot outside of the bus where Jimmy and Clark are shows a woman and a man sitting on the front seats. In the shot inside the bus they disappear.
Continuity mistake: The three baddies arrive at the warehouse, turn on the lights, and watch the supercomputer, standing by two power generators. Cut to a panoramic view of the computer and the lights are out and the baddies gone.
Continuity mistake: When Gus disconnects the computer Superman lies flat on the floor. A shot later his right shoulder is raised, and his body rests on his left side.
Revealing mistake: When Superman fixes the Pisa tower, there's a wire on the left side, most probably the system to move the prop.
Revealing mistake: When Gus flies off with his skis, note that the wooden lattice is already broken before his crash to allow for the stunt.
Answer: The only reason that Gus was working with Ross, Vera and Lorelei was because he stole money from the company he worked at. To avoid going to prison, Gus was forced to do anything that they wanted. After realizing that his computer was designed to do anything it was ordered to, including killing Superman, Gus removed a small screw which shut down the power momentarily but, after the computer brought itself back online, Gus attempted to destroy it with an axe to save Superman. Superman saw this and realised he was wrong about Gus and after the computer was destroyed decided to help Gus find a job.
That makes sense, thank you! Been bugging me for years.
Jen Hen
You're welcome.