Deliberate mistake: At graduation, after Troy is handed the diploma, in the overhead shot the graduates on the left and right stand-up from their seats, then turn and walk towards each other. All their seats simply disappear between shots. Obviously done deliberately for the dance sequence, but a mistake nonetheless.
Deliberate mistake: When Seth Green and Lance pull up to Ian and Felicia, the car being pulled by the carriage should roll a little bit after the carriage stops moving, but instead it stops on a dime when it is only being pulled by rope, and nothing else to stop it with when the carriage stops. (00:42:00)
Deliberate mistake: Wyatt is killed in a park next to El Prado museum (which can be seen in the background). Then S and McQuarry cross the street and appear next to where the bank was. This speeds the pace of the movie, but truth is that the building of the bank and El Prado are 20 minutes walking distance away from each other.