Other mistake: In quite a few shots during the film, it is much too obvious that there are no lenses in Harry's glasses, whereas in previous and following shots the glasses have lenses. A couple of instances are: when Harry drinks the Felix Felicis and when Harry kneels beside Dumbledore, at the foot of the Astronomy Tower.
Other mistake: In the film Harry Potter and the Half Blood Prince, Professor Slughorn (during one of the 'Slugclub' meetings) asks Hermione what her parents do for a living, she replies, 'They're Dentists.' Slughorn and the other wizards stare blankly, not knowing what Dentists are. However, in the film 'Harry Potter and the Chamber of Secrets' in the burrow, we see the magical clock that shows the family's whereabouts, and we see that there is a section marked 'Dentist'.
Other mistake: When Harry and his friends visit the Weasley's house the second time - when the Death Eaters attack - the constellation Scorpio is visible in the sky. Scorpio is a summer constellation. It shouldn't be visible in the winter. Furthermore, it probably can't be seen as far north as England (although I don't live there, so I'm not sure).
Other mistake: While Harry, Ron, and Hermione are walking back from the Three Broomsticks, Ron whispers to Harry about Hermione's earlier comment about snogging, and when we hear Ron say, "As if!" the subtitles read that Harry said it. (00:51:45)
Other mistake: After Ginny sees Hedwig and Harry's trunk at the Burrow, everyone gathers at the staircase and talks to Ginny about Harry's whereabouts, and when Hermione exclaims "Really?" we hear Harry answer "Really!" but the subtitles read that Ron answers Hermione. (00:13:00)
Other mistake: When Professor McGonagall is talking to the trio about the necklace incident and Professor Snape is walking by in the background, he stops just before she calls him over.
Answer: Leaving an untrained young wizard, who obviously has some behavioral issues and has no idea he is magical, alone in the Muggle world would be extremely dangerous. Dumbledore does not yet know that Riddle will become evil, but like any teacher, he wants to give a troubled youth an opportunity to find a new path in life.
raywest ★