Revealing mistake: When Robo gets his arm chopped off by Otomo, he stands up and in Robovision, you see that he needs power, but you cannot see Otomo who is supposedly right in front of him.
Revealing mistake: When RoboCop has his forearm cut off, you can see Robert Burke's arm covered in black material poking out from beind his back. The arm appears again a few times during this scene. (01:21:29)
Revealing mistake: When RoboCop gets his hand cut off by Otomo, he stands up and looks around him. We are given a normal shot of the base, but the screen moves in time with RoboCop's head movements. Surely this shot should have been the 'lined' picture that RoboCop has for his POV shots, and not the normal camera view we were given.
Revealing mistake: When Otomo strikes his sword at the gas station sign, it shows him slicing at the base where the metal ring is. The slice is then shown several feet above the metal ring.
Revealing mistake: When RoboCop storms out of the underground base to the police station, we cut to a scene in the police department. If you watch really closely, nobody actually moves in this scene for about three quarters of a second after the scene starts. People to look out for include the police officer on the far right standing beside a woman in a orange top, (only really noticible in the widescreen version), and the people behind their desks in the background. They are all still or posing, which is amusing to see before they all suddenly come to life. (01:02:14)
Revealing mistake: When RoboCop is covered in flames at the start he walks through a window. Watch carefully, it actually shatters before he walks into it. (00:21:21)
Answer: There was a time conflict. Weller was filming another movie (Naked Lunch) at the same time RoboCop 3 was scheduled for production.
raywest ★