Revealing mistake: When the Enterprise is leaving space dock, look at the right (starboard) side of the ship. You can see the shape of the mounting arm the model was mounted on, even though it was blacked out to look like space, and it also blocked out the bottom of the dock. The footage was reused from Star Trek: The Motion Picture.
Revealing mistake: When the boys are racing away on their bicycles from the Feds, the stunt doubles for Elliott and his friends are obviously way too tall to be children.
Revealing mistake: While escaping from the orgy raid, Valeria stops and kills a few pursuers. However, her last strike never makes contact with the guard.
Revealing mistake: After Flynn, Tron and Ram take their drink, they resume their journey in their stolen Light Cycles. There is a shot of them coming around a corner and riding along a cliff side. If you look carefully (this is painfully obvious if you go frame by frame) they don't actually come around the corner. Their Light Cycles simply appear one by one and they make their turn. (00:50:40)
Revealing mistake: The witch grabs a branded iron and burns the baby's hand. Although she is holding it, the hand doesn't move a single inch, revealing it's a prop.