When Anastasia is kicking the footman into the piano keys, his head hits the keys on the far left of the piano, but higher-pitched notes can also be heard, which could not possibly be heard from the far left end of the piano.
Just before the stepmother locks Cinderella in her room, she asks Gus and Jaq what they are warning her about. When the stepmother takes her key, Cinderella turns around while she says "Oh, no!", but her mouth isn't moving.
Whenever Cinderella's bare feet are shown, she doesn't have toes, except for in the final scene where the Duke places the glass slipper on her foot. The only other human characters to have their bare feet shown, the stepsisters, are both shown to have large, prominent toes.
After Lucifer sees Gus is under the teacup on the right tray in Cinderella's hand, he runs up to the top of the stairs to get him when she passes by, but Cinderella drops off the right tray to Drizella's room first, then the left one to Anastasia's room. Anastasia runs out of her room screaming, showing that Gus was in her teacup (the left tray) when it should have been Drizella running out, or Gus should have been on the left tray.
After Gus drops his breakfast in the kitchen, Lucifer starts to go after Gus. As Lucifer starts to creep up on Gus, Jaq pulls out one of Lucifer's whiskers. But after Gus drops his breakfast again and the next shot goes to Lucifer, Lucifer's whisker is back.
When Cinderella enters the stepmother's room after one of the stepsisters found Gus in her breakfast, she is casting a shadow behind her. When she nears the stepmother's bed, she casts a shadow over the bed, in front of her.
When the Fairy Godmother changes the mice into horses, aside from Gus and Jaq, she changes one mouse with a hat, and another without. However, when they turn back, the two mice besides Gus and Jaq are both wearing hats.
During the ball, the Duke's monocle gets broken during an argument with the King and he looks through the broken monocle at the King as the King leaves. When the Duke goes down to keep and eye on the Prince and Cinderella and as he closes the curtain on the snooping stepmother, his monocle is intact again.
In older releases of the movie, Lucifer's fur is brown when he tries to catch Gus shortly before he turns into a horse and scares Lucifer before leaving for the ball. This has been corrected in later restorations of the movie.
When Cinderella comes down as the Grand Duke is leaving with the slipper, he turns and puts on his monocle. Then after speaking to the stepmother he removes it. When he takes Cinderella's hand to help her down the stairs, his monocle is back on his eye. We never see him replace it.
While the other mice are trying to get food, one of the mice, Jaq, is distracting Lucifer by hiding in a hole in the wall and putting his hat on his tail and sticking it out another hole. Lucifer goes after the hat at the other hole but when the scene shifts back to Jaq, he is still wearing his hat.
When the mice and birds are trying to get Lucifer to let the teacup go, so Gus can get the key to Cinderella, the birds drop some dishes on Lucifer in attempt to let Gus go. The next time we see the floor there are no broken dishes on the floor.
When the horses change back into mice Gus is in back with one of the twins, when we cut to a closeup a second later he is now at the front with Jaq and the other twin who was with Jaq is now in the back with his brother.
At midnight, when Cinderella is escaping in the carriage, we see a full moon low to the horizon. A full moon at midnight must be at its highest elevation with respect to the horizon. Only in polar regions could it be as low as it appears.
When the Duke tells the King that the Prince wants to marry the girl he danced with at the ball (Cinderella), he happily offers to knight the Duke. As a Grand Duke, the Duke holds a peerage; a knighthood can only be conferred on someone who does not hold a peerage (non-noble).
On the palace clock, the Roman numeral 4 is written as "IIII" instead of "IV". However, historically, 4 in Roman numerals was written "IIII". The subtractive system in Roman numerals in which 4 is written as "IV" is fairly recent.
At midnight, everything changed returns to normal, except the glass slippers. This logical contradiction is absent from the original fairy tale, where the slippers are an ordinary gift, not a magical creation, by the fairy godmother.
A big problem with Disney's version of the story is that for all the Grand Duke knows, Lady Tremaine organized a *scam* to marry off her most attractive daughter to Prince Charming, thus making them all members of the Royal Family. Learning from the royal proclamation that any maiden whose foot fits a certain glass slipper will become a future queen, Lady Tremaine could've employed an artisan who spent all night making a near-replica for Cinderella; then put the Grand Duke off guard with Drizella and Anastasia making fools of themselves, which led naturally to the genuine slipper being shattered when in fact the stepmother deliberately tripped the footman. With the Grand Duke thus suitably dismayed, Cinderella would then be able to produce the fake slipper, which of course, perfectly fits her foot.
When the King is dancing down the hall after leaving the Duke in charge of the ball, there is light filtering out of the open door at the end of the hall. When he closes the door, the light is still there.
The goof items below may give away important plot points.
When the mice point out that Cinderella still has a glass slipper (just after midnight), the slipper is on her right foot, and it is established throughout that the slipper left behind is the left one. After that slipper is broken and Cinderella pulls out the right one, it is placed on her right foot; however, and if this is the goof, when she first sits down to have the left slipper tried on before it breaks, she is in the same position, with her right foot held out and unshod.