Audio problem: As McQ is attempting to escape from the hoods by driving down the beach in a 4-door automatic Belvedere, you can hear manual transmission upshifts occurring.
Factual error: The film is set in the 1920's. When the policeman appears towards the end of the film on his helmet is a post-1952 helmet plate with the crown of Queen Elizabeth II.
Other mistake: The Amazon's queen says she pierced Dharma's chest with her spear/lance but he's shown dying from a side wound.
Visible crew/equipment: In the apartment scene with Dustin Hoffman and Valerie Perrine, he prances in front of a vanity mirror, and a big boom microphone is right over his head, hanging deep into the shot, reflected in the mirror. The boom microphone is quickly retracted, so they knew they had made a mistake, but the shot remained in the finished film.
Factual error: At the end of the movie, Mame takes Peter with her on a trip to Siberia. However, at this point in the timeline, it's the late 1940s, meaning that Stalin was still in power, so even Auntie Mame would be crazy to think of vacationing in Russia. Not to mention the difficulties of getting Peter a visa to travel to the USSR at the last minute. (In the stage version, the destination was India, rather than Siberia, which makes a lot more sense).
Visible crew/equipment: There's a scene where the airship Hyperion is flying low among the icebergs and the Captain is bragging about his piloting prowess. In one shot the ship emerges from behind a pillar of ice, and the shadow of a large piece of overhead rigging falls over the top of the miniature berg.
Revealing mistake: During the chase that opens the movie, the guy trying to escape shuts the door labeled "Back Stage" behind him. The various goons try to push it open, but only the badass villain with the charismatic afro can do it using his palm strikes. Sort of though, because just before he shows up in front of the door, you can see the door was unlocked and opened under the push of the normal minions, with the light fully showing between door and frame. (00:03:10)
Continuity mistake: When Julie is running up the stairs to catch up with Celine, in the shot where the camera is positioned at the bottom of the staircase, there are two people ahead of her walking down the steps. The camera then changes to a closer angle in front of her, and the two people walking down the stairs have disappeared. There is also one completely different man who has appeared on the steps. (00:09:25)
Continuity mistake: In the opening scene, Irwin Ingham's big scarf is wrapped around his neck in ever-changing fashion as it can be spotted looking at the striped area being at different height each time. (00:03:40)