Deliberate mistake: During the early rehearsals for "Yip Yip Yaphank", a group of men are around the piano singing "God Bless America", and we hear the following lyrics: "Stand beside her/And guide her/TO THE RIGHT/With a light from above". This is NOT an error; I'm guessing that those were the actual lyrics of the rough draft, with the capitalized line above changed to the present "Through the night/With a light." at a later date. (00:14:50)
Deliberate mistake: When Eric's ship blows up, his statue bobs up and down. A statue this weight would not be able to bob up and down for even a second. It would just sink straight to the bottom.
Deliberate mistake: Riccardo is a stowaway on the ship, but he was standing on the dock when it pulled away.
Deliberate mistake: Foils, rapiers and other fencing weapons did not appear before around the 16th/17th century, yet the main characters (in an approximate 8th to 10th century setting) use them extensively. I know that back in the days when the movie was made, the swashbuckling genre was quite popular, but it still is a reality error.
Deliberate mistake: During Lansbury and Dr. Brown's dance scene under the water, the drawings behind them (with couples of fishes sitting on their seats) are a still drawing, no animation at all.
Deliberate mistake: When the saloon patrons pour through the swinging doors in pursuit of Packer, the same people are seen repeatedly. A relatively small number of extras are running around to the rear of the set and re-entering through the back so that they will appear to be a larger crowd of people.
Deliberate mistake: When Jafar sees Aladdin reflected in Jasmine's crown, Aladdin is the only thing visible. This isn't possible- we should have also seen the background of the room, the objects around him, etc.
Deliberate mistake: When Hillary and CC are looking at Victoria after she's born, the baby Hillary's holding looks like it's several months old, not a red and pinched-looking newborn.
Deliberate mistake: After Sharpay falls into the pool, when Gabriella dives in it is an obvious stunt double for the actress. (00:16:40)
Deliberate mistake: During the finale of "One," near the end of the number when the entire cast and all of the extras, dressed in gold lame tuxedos, are doing the last kick line before the credits, one of the dancers (second row, third from the right) falls down and gets right back up again. While this mistake wasn't "deliberate" as such, it was probably simply prohibitive to film the entire kick line over again for the sake of the one fall that is barely noticeable, so was deliberately left in.
Deliberate mistake: During the first aerial angle of the pirate ship they are heard singing, but the ship is empty. Most surely due to the complexity of drawing detailed tiny pirates.
Deliberate mistake: Before Dorothy is sent to Kansas there's a close-up of her shoes. All of the group's feet, Glinda's dress, and the rest of the elements around are gone and replaced by a black background. Despite being a deliberate directorial decision to give the shoes a more dramatic focus, it is really awkward to see everything disappear, nevertheless.
Deliberate mistake: When the blonde girl is doing a strip tease, she has long hair which reaches far down her back. However when they show a flash shot of her breast as she spins, her hair is only to her neck. Obviously a double.
Deliberate mistake: I know this has been disregarded for the fun effect, but gasoline motors require air to work. When Edgar drives his tricycle into the river while being chased by Napoleon and Lafayette, it should have stalled and stopped working.
Deliberate mistake: When the gangs meet in the toilets to set a date for the brawl, the mirror on the left is the only one opaque, most surely to avoid reflections of the filming crew.
Deliberate mistake: Throughout the movie we hear every animal (and insects/arachnids as is the case with Charlotte and her offspring) with one exception. Every time Charlotte catches her meals in her web we never hear the fly or other insect she is descending upon cry for help, or plead with her to be spared. This is deliberate due to this being a kid's film but still bears noticing as a mistake due to the fact that they are the only ones rendered mute for plot convenience.
Deliberate mistake: In the first shot, we see Farley Flavors sitting in what looks to be an editing room, smoking and waiting for the show to start. As we pan out, we continue to see him smoking, through a giant heart shaped window. A few moments later, we see the same heart shaped window, only now with a red screen over it. (00:01:15 - 00:03:10)
Deliberate mistake: Several times, you see an exterior shot of Nathan's house, and it is very clear that it is the same shot being used over and over, sometimes reversed.
Deliberate mistake: When Big Gay Al sings his song, he sits at the edge of the stage. In a wideshot the soldiers are just watching, yet in a closeup they're all waving lighters. (00:59:25)
Deliberate mistake: Gonzo and Rizzo are selling apples in the beginning, including the Red Delicious cultivar. That wasn't invented until the 1880s and the story is set sometime in the first half of the 1800s. Most likely intentional as they are the narrators.