Deliberate mistake: All Minor Hockey Leagues in North America require players to wear visors with their helmets.
Deliberate mistake: Baron Munchausen sends his courier, Berthold, on a one-hour errand to procure a bottle of the finest Tokay from the imperial wine cellars in Vienna. Berthold returns with the bottle within the hour and (in one continuous wide shot) hands the bottle to Baron Munchausen, who then hands it to the Sultan, who effortlessly plucks the cork from the bottle with his fingertips and pours a glass for himself. But there is no way the Sultan could simply pluck out the cork with his fingertips in one move; this extremely valuable bottle of wine is visibly sealed (in every shot) with a thick, air-tight red wax. This wax must first be cut and peeled away to access the deeply-embedded cork, and the cork must then be removed with a wine key (corkscrew). The action of properly opening the bottle would have required more time than the entire scene itself; so, to expedite the flow of the shot, director Terry Gilliam deliberately chose to forego a proper uncorking.
Suggested correction: You're ignoring the fact that the entire scene is a story the real Munchausen is telling from memory. There are many fantastic elements that do not hold with reality, like him riding his horse out of the window, falling several stories, and landing safety, or Adolphus being able to see and shoot to the other side of the world. The bottle is simply an example of Munchausen not adhering to reality.
In any event, the Sultan's effortless uncorking of the bottle was a deliberate mistake intended to allow a whole series of actions to occur sequentially in the single wide shot in less than 5 seconds.
Yet, at the end, Sally addresses Baron Munchausen directly and asks him the question that the audience has been wondering throughout the whole movie: "It wasn't just a story, was it?" The Baron solemnly shakes his head, affirming that he was telling the truth all along, regardless of how fantastic it sounded. This point is often missed by the movie's critics.
The point I raised wasn't that the Baron's story wasn't true, but rather that he embellished it.
Deliberate mistake: Near the end, after the case is dismissed, people are celebrating, and we see a reporter talking, with snow flying around him. Cut to another shot of people watching a television. The snow has disappeared from the reporter's shot. It's likely that, since the snow was added in post, the filmmakers forgot to include it in that one shot.
Deliberate mistake: Just after arriving in the 21st century, Thibault and André enter an elevator and scare away its occupants. Attempting to chase them, the elevator doors close despite their attempts to keep it open. Elevators have a safety mechanism which opens the door when they encounter resistance. This was ignored deliberately in the film for comic effect.
Deliberate mistake: When Kalidor beheads a warrior and when Sonja beheads the wizard, both heads don't fall sideways as they should, but instead fly upwards, revealing they were tossed by someone offscreen - which looks more impressive, indeed.
Deliberate mistake: When young Odette is sliding down the banister, and gets stuck spinning around the end of it, it would be impossible to spin like that without her legs hitting the rail that she just slid down.
Deliberate mistake: When Violator turns back into Clown in the alley, watch closely. You can see his shadow beneath him for a few seconds as he's transforming, and it doesn't match the transformation of the giant monster into the Clown... it's just Clown's regular shadow from the actor standing on-set. More than likely, it's a shortcut for the effects - they didn't bother rendering a simulated shadow. You have to look kinda close to notice it the first time, but once you see it, it's obvious.
Deliberate mistake: When C-3PO, R2-D2 and the younglings are driving through the battle zone, Anakin Skywalker and General Grevious can be seen battling. Later, Darth Vader can be seen on Hoth. This would be impossible due to Anakin Skywalker being Darth Vader. (00:08:50 - 00:12:20)
Deliberate mistake: The surviving passengers are all awoken from a deep sleep after Dinah realises the other passengers have gone. Yet none of them appear drowsy or tired and none of their eyes appear strained, despite having just woken up so suddenly. (00:09:20)
Deliberate mistake: In the end scene at the TV set, Scrooge tosses a coin out the window, and the camera follows the coin as it falls in slow motion. The people in the control room also watch this on their monitors. Problem is, this is a live broadcast and filming/watching something live in slow motion is impossible.
Deliberate mistake: Elizabeth will not be able to save Mateo from falling backwards into the fire pit by grabbing his hand or pulling him back after his whole body is suspended over the edge. (01:13:47)
Deliberate mistake: Instead of being a specific language, Edward has an English to Asian dictionary. I've heard this was done to prevent a particular time period from being established. (01:12:55)
Deliberate mistake: When Flash is at the coffee store, the pavement is dry. When he exits the place dressed as The Flash, it's wet for cinematic purposes, but a mistake nonetheless.
Deliberate mistake: When Spidey jumps on the hood of the truck, Rhino squirts him using the wipers. Funny, but he can do that only because the detergent sprays forward instead of the angle actual windscreen washers are pointed at. (00:12:50)
Deliberate mistake: When Larry and the two moving men are first bringing the mattress through the doorway and it gets "stuck," the camera placement makes it pretty obvious that the mattress isn't really stuck. There's far too much wiggle room on either end for it to be "stuck." (Obviously it needs to be stuck for the scene to work... but still a weird inconsistency).
Deliberate mistake: When Alice is about to meet the queen she hides the brush covered in red paint under her dress. The brush later disappears plus Alice doesn't have any stains on her clothes.
Deliberate mistake: The ghost opens Nikolaj's bedroom door an inch or so, yet there is enough light emitting onto the hallway floor for the door to be open about halfway. After the door closes, the light on the floor continues to gradually fade towards the closed door. (00:17:05)
Deliberate mistake: When the two security guards inside Firebrand alert the other security about David being on the roof, a news reporter overhears, announces it and everyone looks up. The news channel then shows an above angle shot of David standing on the ledge within a second, but how did the news channel manage to start filming David standing on the roof that quickly or even manage to film from this angle? David going up onto the roof was entirely unplanned and within a few seconds of anyone realizing he was on the roof, there is suddenly a news helicopter from above filming the entire thing. It could not have been filmed from the ground because the news is filming an above angle shot and would have been too far away to film. This was probably done intentionally to increase the drama, but still makes little sense. (01:16:50)
Deliberate mistake: Hansel will die if he doesn't take his medicine for 4 hours, but after hanging overnight in a tree he shows no signs of needing.
Deliberate mistake: In the housing block that Dave's house is in, the house numbers do not match - because In one shot of Claire walking past Dave's house, you can see that the house numbers are in the 1500's - one homes number is clearly 1516. However Dave's house number is 1958. However this is a deliberate mistake as the 1958 on Dave's house is a reference to when the Chipmunk fever was born. (00:23:50 - 00:32:35)