Continuity mistake: When the volcano erupts, there's suddenly a lot more snow on the crater.
Continuity mistake: When Lois opens the terrace doors in the hotel suite, the angle changes and the furniture on her right moves several meters to the left, appearing close to Lois.
Continuity mistake: In the gym, a man leaves a towel on a low wall. Watch the blue and grey stripes and you'll notice that its position is different between shots.
Continuity mistake: When Superman flies away from the tower holding the elevator, the first angle shows him leaving towards a 10 o'clock direction. A frame later the position of the cable shows him leaving to a 7 o'clock direction.
Continuity mistake: When Nuclear Man and Superman fall off the balcony and fight, the position of their bodies has no continuity in the wide and close shots.
Continuity mistake: In the quarry, the cop on the right's hat has two strings around the top, the upper one dissapears depending on the shot.
Continuity mistake: The UN building that Superman walks towards and the one he arrives at in a new shot look entirely different.
Continuity mistake: When Luthor introduces Nuclear Man to Superman, a towel on a chair changes from ironed and flat to a big bundle in less than a second.
Continuity mistake: When Nuclear Man is about to land on the Great Wall, the aerial view shows it's empty; a second later it's filled with people.
Revealing mistake: After Nuclear-Man kicks Superman in the air after putting the Statue of Liberty back, Superman does flips and part of him disappears.
Revealing mistake: When the subway train is supposedly running wild, watch the man to the left of Lois: He throws Lois's book violently away on the sly, as if the (fake) rumble inside the train had done the mess.
Continuity mistake: Nuclear Man sends the 2 police cars back and the one on the right skids and faces slightly to the right, but a second later, when they explode, both cars are perfectly aligned.
Continuity mistake: When Lacy shows the mock front page of the Daily Planet she holds it covering the red circle on the top right. A frame later she's holding it several inches down.
Continuity mistake: When Nuclear Man sends the police cars back, there's a man close to a mailbox on the left. There's a very brief cut before the cars explode but when the explosion takes place, the man has vanished.
Factual error: Superman and Nuclear Man fly around the world fighting at incredible speed. Everywhere they go, including places as widely spread as New York and China, it's daytime.
Visible crew/equipment: When Nuclear Man's laser beams send Superman flying away on the moon, the shadow of the crane moving him is visible.
Continuity mistake: Nuclear Man lands on a street surrounded by skyscrapers. In the following shots where he destroys everything, the right side of the street is the same, but the left side is totally different: small houses, sunnier, signs on the walls.
Continuity mistake: While the volcano explodes close to the Italian village, a man jumps off a balcony but disappears just a frame later from the following wide shot of the place.
Continuity mistake: A couple seconds after Lenny insults Nuclear Man, when he is about to be lifted up, the place he stands in is different from where he was before.
Audio problem: When Lex is giving instructions to launch the missile, a young man puts on his earphones and talks to Lex, but his mouth doesn't move.
Answer: There appears to be multiple reasons. They had creative differences, ultimately resulting in a poorly received movie. Kidder said Reeves, who co-wrote the story, had an inflated ego and clashed with Furie.
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Moreover, Mark Pillow, who played Nuclear Man, claimed that working with Reeve was quite intense.