Continuity mistake: Watch when Jack Lemmon falls into the giant cake at the beginning of the pie fight scene: he destroys all but a thin vertical pillar on the right side. During the fight, we see two other angles on it before the cake is fallen on again - in a shot from the exact same angle as before - but this time a large portion of it has somehow restored itself, and in a completely different configuration.
Revealing mistake: In the final shot of the film the model makers neglected to include the antenna at the top of the Eiffel Tower, seen previously on the real tower in the establishing shot of Paris. (02:31:20 - 02:37:10)
Audio problem: In the beach scene near the beginning, Leslie Special comes to a screeching halt in front of Leslie's tent on a bed of sand. Can't burn rubber there.
Continuity mistake: As the bakers assist the Prince to get out of the cake he's fallen into, the General begins to descend the stairs to the kitchen. Yet the general is not seen again until just before the Prince hits him with a pie.