Continuity mistake: When Superman arrives at Pisa for the second time, the sky changes from violet to blue.
Other mistake: The movies show that Superman can talk and live in space as normally as on earth, with no extra effort needed. Therefore, the scene of Superman choking and suffering inside a shield/ bubble with no air is totally senseless. The Krypotnite laser which does choke him appears after he has destroyed the bubble.
Visible crew/equipment: Lighting screen reflected on the police car's trunk by the burning factory.
Continuity mistake: In the bar, while bad Superman is destroying the bottles, the way they are placed and the ones that are broken or undamaged keeps changing between shots.
Audio problem: Inside the subway, Rikki's voice is heard but his mouth doesn't move.
Continuity mistake: Bad Superman punches Clark and he lands by a car door. In the next shot the door has magically moved on top of him, which makes Clark take it off of him.
Continuity mistake: When Clark is choking bad Superman, his right hand cleans itself after Superman disappears.
Continuity mistake: When Superman lands in Ross's attic, a chair moves to the left between one shot and another.
Continuity mistake: While bad Superman is in the bar, the whiskey bottle's label faces the window. From the window's point of view there's no label seen.
Continuity mistake: On the Grand Canyon, when Gus is about to get on the donkey, the first shot shows him several meters ahead of Vera. The next aerial angle shows him very close and parallel to her.
Continuity mistake: During the credits, a red and white pole with a light on top appears to the right of the crashed green car.
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.
Continuity mistake: In the wheat field, after Superman brings Ricky, the upper sleeve from the pullover tied around Lana's neck changes size after Superman leaves.
Revealing mistake: When the two Supermen are fighting, towards the end Clark chokes evil Superman. In this shot you can see where they cropped a stuntman's hands in the place, where Clark's hands would be, in order to have Christopher Reeve play both parts.
Audio problem: When the power goes out all over Metropolis because of the Super Computer, Ricky and Lana are in the subway and panicking. Ricky cries out, "Why aren't the lights going on, " but you never see his mouth move.
Continuity mistake: After Superman fixes the oil tanker and touching the oil soaked steel, he waves goodbye to the sailors and his hands are clean.
Continuity mistake: A thief comes out of the Century Savings Bank, but the money bag he holds reads Metropolis Bank.
Continuity mistake: From the inside, the sign on Archibald Data Processing has a square thing on top of the first and last letters. From the outside it doesn't.
Continuity mistake: When the roller-skate girl grabs the trolley, the cups and food on the upper plate fall. A frame later they're all back on.
Continuity mistake: When the roller-skate girl grabs the trolley. In the close ups she is bending to the front, in the wide ones standing straight.
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.