Continuity mistake: At the Ministry of Magic, as Yaxley is reprimanding Ron, who is disguised as Reg Cattermole, the initial on Yaxley's Ministry tie pin changes direction. In one shot, the letter "M" is tilted to the left, and in a subsequent shot, it's slanted in the opposite direction.
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.
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.
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: After Ron destroys the Horcrux, Harry goes to sit beside him. The distance between him and Ron increases in the next shot.
Revealing mistake: Watch as Ron pulls Harry out of the icy lake and leans Harry up against a large root. When Harry's back comes in contact with the root, it wobbles. Unless Harry weighs a couple of times more than he does, the root wouldn't flinch.
Continuity mistake: When Mundungus is confronted about the locket, as he says, "Could I help it if Mad-Eye fell off his broom," Ron places his hand on the chair with his hand facing away from Mundungus. Depending on the angle of the following shots, Ron's hand is either facing Mundungus or facing the opposite way.
Continuity mistake: When Hermione apparates herself, Harry, and Ron away from the wedding, she does not have her beaded bag, nor is it on her person when they first appear in London. After ducking into the alley, she suddenly has it in her hand. From then on, she always has it.
Continuity mistake: After Ron pulls Harry out of the hole in the icy lake and leans Harry up against a rock, we see Ron back up a few feet. When it cuts to Harry getting up, Ron is much further away.
Factual error: In the scene where Harry and Hermione are dancing in the tent, a radio is on. The song played is "O Children" by Nick Cave & The Bad Seeds, which was released in 2004. However, Harry Potter and the Deathly Hallows takes place in 1997-1998, considering that later in the film the graves of Lily and James Potter give their death year as 1981. As Harry was one year old when his parents died, this means that he was born in 1980, and thus the film itself must, like the book, take place in 1997, when Harry is seventeen. This makes it impossible for "O Children" to have been on the radio at the time.
Continuity mistake: When Harry dives through the hole in the icy lake, water floods over the edge of the hole, and flows over a large part of the ice, dampening the snow on the ice. When it cuts to Ron pulling Harry out of the hole, the wet snow around the hole has decreased by several feet, only surrounding a small part of the hole itself.
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: In the first shot of Harry, Ron, and Hermione at the café after escaping the wedding, Harry asks if they should go back. Then the waitress walks past the camera. When it cuts, the waitress walks past the same spot again.
Continuity mistake: When Hermione picks up the "Albus Dumbledore" book in Bathilda's house, she picks it up with her left hand, while her right hand is holding her wand only. When it cuts she is holding the book with both hands.
Continuity mistake: When Harry holds the mysterious locket up in front of Kreacher, the chains are together from Harry's POV and separated from Kreacher's.
Continuity mistake: When Mundungus arrives at the house with Kreacher and Dobby all over him, the pot, glassware, wire basket, bottle, etc. on the counter beside the sink disappear, reappear and/or change entirely in the close-up and following shots.
Continuity mistake: When Harry is holding his wand over the icy lake, the light is reflected on the surface. When it cuts to a closeup the reflection is all gone.
Continuity mistake: When Harry, Hermione and Ron confront Mundungus about the locket, he sits down in the corner chair and the side table is beside the chair, with the mess of Daily Prophets on the floor in front of the table. However, in the following shots the table is 3-4 feet away from the chair, against the wall, with one Daily Prophet between it and the chair.
Continuity mistake: In the diner, when both Hermione and Ron aim their wands at Dolohov, the boxes of Amaretti cookies explode off the shelf behind him. However, in the following shot one Amaretti box (facing the wall) is still on the shelf, then vanishes and reappears once again.
Continuity mistake: In the scene in the Cappuccino Cafe, Hermione performs "Petrificus Totalus" on a Death Eater and Ron talks about killing him. Harry says, "It's best we wipe their memories." As he says that, he is looking down at the Death Eater. In the very next shot, his head has slightly moved and he is looking straight at Ron.
Chosen answer: Because Harry already knew where the camp was. The protection spells they use (Harry is shown at one point casting them as well) seem to be sort of like the Secret Keeper spell. If you cast them or they are cast on you, it allows you to see through the spells. Also, don't forget that the deluminator led Ron right to the general vicinity of the camp and that the Snatcher team could smell Hermione's perfume through the spells earlier.
Guy