Continuity mistake: When Xenophilius Lovegood is drawing the triangle in the Deathly Hallows symbol, he starts with the left side, moving the pen DOWN on the page. The shot changes to Harry, Ron, and Hermione, but we can still hear him drawing and the sound indicates that he never lifts his pen from the paper. However, when it cuts back to him finishing the symbol, the right side is already drawn and he is finishing the bottom. With the way he was drawing it, he should have drawn the left side first, then the bottom, and finally the right. However, this would not be possible to do unless he lifted his pen from the paper, which, as stated before, the sound indicates that he did not do.
Revealing mistake: Throughout the whole movie it can be seen how Harry's glasses don't have the glass lens on them. Only in two or so scenes do they appear.
Continuity mistake: In the forest, when Hermione is sitting with her back against a tree, reading, the book changes position between shots after Harry walks over to her. In a close-up, the top of the book is over her knees, in the following wide-shot, the book is below her knees, and then moves back to its original position in the next shot.
Continuity mistake: In the second to last shot, where Lord Voldemort is drawing the Elder Wand out of Dumbledore's hands, and then thrusts the wand into the air, Lord Voldemort's arm has hair on it. In the book, he is described as completely hairless, and in every other shot in every other movie, they have been careful to remain true to this.
Factual error: During the scene when Harry and Hagrid are on the motorbike going through a tunnel, the bus signals that it is going to Dartford. Both of the tunnels at Dartford carry north-bound traffic, going away from Dartford - all south-bound traffic, towards Dartford, travels on the bridge (visible in some shots). No traffic enters the tunnels heading south-bound towards Dartford.
Continuity mistake: As the Death Eaters disrupt Bill and Fleur's wedding, Ron holds Hermione's right hand and Harry holds her left hand as she disapparates with them in tow. However, when they apparate onto Shaftesbury Avenue, Ron and Harry's positions have switched, now Harry holds Hermione's right hand and Ron holds her left hand.
Continuity mistake: Near the end, when Hermione jinxes Harry's face to disguise him, she removes his trademark glasses to hide his identity and shoves them into her own pocket. Harry is still without his glasses during the confrontation at Malfoy Manor where his identity remains in doubt (his glasses would give him away). However, as Wormtail (Pettigrew) is taking both Ron and Harry to the cellar, Harry's glasses are suddenly back on his face, even though Hermione was separated from the group.
Continuity mistake: When Harry, Hermione, and Ron confront Mundungus about the missing locket, Mundungus knocks over a tall stack of Daily Prophets on the floor. However, when Mundungus puts the Daily Prophet (with Umbridge on the front page) on the table, the stack is back upright behind Hermione.
Revealing mistake: When Harry walks across the frozen pond, both in his shoes and when he is barefoot, there are no footprints left on the ice. The pond is covered with a light snow, that Harry brushes away to see the Sword of Gryffindor beneath the frozen surface. The snow would show any tracks.
Continuity mistake: When Hermione and Harry are sitting on the rocks by the cliff, Hermione is putting down a closed book. When the camera angle switches to seeing Hermione from behind, it appears the wind has blown the book open, but when the camera switches back to a front view, the book is closed again. One final switch, and the book is open yet again, flapping in the wind.
Continuity mistake: When Hermione removes her parents' memories at the start of the film, she points her wand at them and says "Obliviate", turning her wand hand so that her palm faces inwards/upwards. In the very next shot, however, her palm is facing outwards/downwards, with no time to change in between.
Continuity mistake: Early in the scene where Hermione is cutting Harry's hair in the tent, Ron is lying on the bed with his arm in a sling and wearing what looks like a sweatshirt. In the shot where he comes in and says, "The sword was stolen," he is in a different outfit and his sling is gone. Since we could heard the scissors cutting Harry's hair at the beginning of the shot, we know that Ron was wearing something different and was in a sling just a moment before he walks in.