In "At the End of the Day" when all the women quickly form two rows the positioning of Fantine and the factory women standing on either side of her changes about three times.
When Gavroche first comes up from inside the elephant, he is wearing only a blue jacket. In the next shot, He is wearing a brown blanket. In the shot after that, it has disappeared again.
When we first see Enjolras speaking before the crowd during "Look Down", he and Marius are holding pamphlets in their hands. When Enjolras sings his line "Where is the king who runs this show?", he raises his hand above his head and the camera does a quick cut for a close up -- revealing that the pamphlet has vanished from his hands.
During the final scene, the sky changes between shots from being cloudy to having few or no clouds.
When Javert arrives back at the barricade, the gun disappears and reappears in his hand.
The story takes place in 19th century Paris but all the French characters speak English instead of French, or German or Italian, which were the two most important minority languages in the city at that time. However, this is not a mistake by the filmmakers; it is extremely common for films about non-English speaking people that are made for English-speaking audiences to use English instead of the non-English language that the characters would actually be speaking in real life.
Very near the end of the song "Stars," a shot from behind Javert shows he is facing Notre Dame and the moon is in the sky to his right. Although the moon is to his right and illuminates buildings in the background from that perspective, the light reflected off of Javert's forehead is coming from his left.
When Fantine sings 'I dreamed a dream', not all of her teeth are discolored. White teeth are visible (from her canines backwards) towards the end of the song.
The movie acknowledges the novel's country of origin by having all street signs, postal notes, and documents in French. Except in "Master of the House," where signs for "glasses" and "eyes" and a menu are written in English.
The calf seen wandering in the barricades scene is a whitefaced Hereford poll. That breed did not exist before the 1880, and did not reach France until the 20th century.
When Javert gets the letter from Paris informing him that "Valjean" has been caught, the tricolor French republican flag is seen hanging in the street. But this scene takes place in 1823, during the Bourbon restoration. During this time (1815-30) the tricolor was not in use.
During the final act (1832), Javert wears the medal of a Chevalier of the Legion of Honor. The medal is the modern version, a five-pointed Maltese Cross mounted on a green palm wreath. The period version had a bronze wreath.
The bishop is wearing incorrect liturgical vestments. He is shown wearing a dalmatic which is the vestment for a deacon with a stole worn 'priest-wise' on top. A french bishop of this period would have worn a 'fiddle-back' Latin chasuble with crossed stole underneath.
When a young child hops on the back of a horse drawn wagon, very clear views are given of the caliper disc brakes on the rear axle of the wagon. Brakes like this were not used until 1890 at the earliest.
When Thénardier is singing "Master of The House" and changing his hat/removing his glasses, he is visibly not moving his lips even though the song is playing.
When Jean Valjean "dies" you can see Fantine (Anne Hathaway) bending down and crawling out of shot.
Thernadier speaks in different accents throughout the film; sometimes he has a British accent while other times he uses a comically bad French accent.