Continuity mistake: The location of the staircase leading up to the supercomputer's control console changes. When they first enter the computer, it is at the back of the computer behind a lot of electrical machinery and circuits. When Ross comes down to try and get the screw out of Gus's mouth, the staircase has moved right next to the entrance of the computer (where Vera gets turned into a robot later on).
Continuity mistake: The firetruck's ladder Jimmy climbs up during the chemical plant fire changes between shots. In the first shot its a white-framed ladder at a pretty shallow angle. The ladder in the second shot changes to a black and orange one which is at a much steeper angle and the rungs are spaced further apart. Also in the second shot he is much closer to the top of the ladder than the first shot, and there is no way he climbed up the ladder that fast.
Continuity mistake: When the Pisa tower seller sees Superman, the wineskin swaps sides between shots.
Continuity mistake: After Gus unscrews the computer, the lights go off and Superman's corner becomes dark. From the opposite angle it's perfectly lit.
Continuity mistake: After Clark kills the bad Superman, he has dishevelled hair but after he flies it's now perfectly combed again.
Continuity mistake: When good Clark is on the trash compactor about to be covered in metal parts, he lays on a blue car hood. Depending on the angle the hood is barely rusty or very rusty.
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: During the tablecloth scene, while Ross listens to Gus, the coffee pot located a meter to the right appears right behind Ross between one frame and another.
Continuity mistake: At the acid storage room, while the chemist says that the temperature can't rise to much you can see the needle on the background way to the right revealing it's hot. But the next shots of the needle show it on the very left first and rising on the second.
Continuity mistake: When the green car crashes, it leaves a lot of rubble in front of it. In the wide shot, the street is clean.
Continuity mistake: When Superman flies back to Pisa, Giorgio, the seller in the back, is wearing a T-shirt. In the close-up he wears a shirt.
Continuity mistake: The second hole Gus makes with the axe on the laser ball is smaller a second later.
Continuity mistake: Before Superman fixes the Pisa tower, the Italian seller is seen holding a statue by its base. A frame later he holds it by the side.
Continuity mistake: When Clark is waiting for the steel lid to crush him, he raises his arms up. In the next angle they are down and close to his side.
Continuity mistake: When Gus takes the tablecloth off, he walks on top of the fallen stuff to talk about Superman, and then the amount of stuff left behind keeps changing between shots.
Continuity mistake: When the bus to Smallville pulls over, the red ambulance passes by twice.
Continuity mistake: After Clark kills bad Superman he rises and the shot changes. His tie knot is now tilted to the right.
Continuity mistake: Amount of snow on the railing changes after Gus flies through with the skis.
Continuity mistake: The two firemen pointing at the lake are standing close to each other. In the wider angle they are much farther away.
Continuity mistake: When Vera is getting sucked into the computer, she has white gloves on. Seconds later, during her robot transformation, there is a full screen close up of her hand without any glove. Then, when Vera emerges from the wreckage of the computer a few minutes later, she has her gloves on again.
Answer: There were rumors that Hackman was angry with the Salkind Brothers (the producers) for firing director Richard Donner, though Hackman later disputed saying that. His explanation, though he may have been downplaying the real reason, was that he had a number of other movie projects at the time, and he also did not wish to continually play the same villain in an ongoing movie series.
raywest ★