Trivia: Just after the Jet "lands" in the stadium, the film shoots back over to Lex and his gang at the mansion. We see a closeup of the battered miniature town and there is a downed sign showing the name of the model railroad city, "Smallville."
Continuity mistake: In the scene where Lois Lane is holding her son as Lex Luthor is revealing his plan to her the ring on her left hand switches back and forth between her middle and ring fingers. (01:25:05)
Continuity mistake: Near the end of the film when Lois makes to leave the hospital room after visiting Superman, she takes hold of her son's left hand with her right - meaning he should walk out whilst at her right side, furthest away from the hospital bed. In the next shot, both Lois and her son have swapped positions. (02:00:00)
Continuity mistake: In the scene where Richard finds Lois and the son on the yacht, he hugs the boy and you can see that one of the drawers is open. When he looks up at Lois, the drawer is now closed. (01:46:30)
Continuity mistake: When Lois Lane and Lex Luthor are talking on the ship, the knot on his tie changes throughout the scene.
Continuity mistake: When Superman grabs the falling sculpture-globe the aerial view shows the hood of the cab on the left is undamaged. From a ground level view, the hood is severely damaged. (01:44:35)
Continuity mistake: In the scene where Superman is trying to prevent the plane from crashing he is holding the nose of the plane and bits of it start to crumble in and fall apart or away. Once the plane is safely on the ground within the ballpark the scene shows the plane from the side where there is no damage to the nose. (00:40:15)
Continuity mistake: In the scene when Lex is testing the kryptonite at the basement of the mansion, after the power outage, he is standing directly in front of a square yellow sign. Cut to a wider shot, and he has moved left and Kitty is now in front of the sign. Cut again and Lex is back in his first position. (00:32:15)
Continuity mistake: When Superman picks Kitty up from the car to take her to the hospital, her white skirt is way above her knees, revealing the top of her stockings. Superman's hands are on her stockings. When he starts to fly up, the skirt now covers her knees, with his hands on the fabric. (01:00:10)
Continuity mistake: During the robbery, the machine gun's ammunition belt is on the weapon's left side. In one brief shot, it's on the right. This shot is flipped. (00:55:35)
Continuity mistake: The writings on the note Lois faxes to the Daily Planet (with the coordinates) change from when she writes it to when Jimmy sees it through his camera. For example, the 'N' is much smaller and the 'P' is fatter in the faxed version. (01:31:45)
Continuity mistake: After the plane has landed in the stadium and Superman is checking if the passengers are all okay, note the speaker's glasses. They alternate between being very crooked to being perfectly straight. (00:41:15)
Answer: There are two stories: a) the suit was made by Martha Kent from the blankets which came with Superman when he was a child and these blankets got superstrenght from the sun too. b) Superman generates an aura which protects him and his suit against such forces. Both stories can be true: either the suit itself is weakend by the kryptonite or Superman's aura was weakend by it. Currently it is said that the blanket-story is the correct one. Also, they don't actually cut it off him - it appears to open along a predefined line (coupled with someone exclaiming "got it!"), presumably the method Superman uses to get into the suit himself.
Bjoern_Buller