Corrected entry: When Harry gets the Advanced Potions Making book, "This Book is the Property of the Half-Blood Prince" is on the first page. A little later when Hermione and Ginny want Harry to turn the book in, Ginny grabs the book from Harry and looks at the last page and reads "This Book is the Property of the Half-Blood Prince".
Corrected entry: Harry and Dumbledore apparate from the tube (train station) at few minutes after 11 p.m. (as evidenced by the date that Harry made with the waitress for when her shift ends at 11). However, they apparate to the town where Prof. Slughorn is hiding and the grandfather clocks reads approximately 10:26 p.m.
Corrected entry: When Harry is preparing a new Quidditch team, and after Ginny shouts for everyone to shut up, there is a man walking behind the goal posts in the background. Normally this could be just any other character, but the man is wearing regular trousers and a long shirt or jacket.
Corrected entry: At the top of the Astronomy tower when Dumbledore is talking to Harry about the Horcruxes, as Harry walks towards Dumbledore you can see two people, either crew or extras, walk behind the "wall" to the right of the shot.
Corrected entry: When Snape appears after Harry has used Sectum Sempra during his fight with Draco in the bathroom. Harry leaves the bathroom and there is an extra or a crew member standing against the wall.
Corrected entry: When Tom Riddle is talking to Professor Slughorn about horcruxes, Slughorn mentions that you have to kill to make a horcrux as it rips the soul apart. Tom Riddle says, "Can you only split the soul once, for instance seven?" This shows that Tom was planning to make seven horcruxes, however he only intentionally created six horcruxes and as Dumbledore said in 'Deathly Hallows Pt 2', "You were the horcrux Voldemort never intended to make, Harry". Surely Tom would have said six horcruxes then, not seven.
Corrected entry: When Harry and Ron talk in the bedroom, Harry is watching Draco where he goes with the special map of Hogwarts, the name of Draco on the map is misspelled Malpoy.
Corrected entry: In the scene where Draco attacks Harry on the Hogwart's Express, it appears that they shot to scene at both ends of the train compartment and then spliced the different takes together. If you watch the numbers on the wall above the seats, they bounce back and forth from low to high numbers.
Corrected entry: After Draco is escorted out of Slughorn's party by Snape, and Harry begins to spy on them, you can see crew rugs used to quiet Draco and Snape's footsteps. The same rugs are visible earlier in the film when Harry and Ron walk down a corridor after Slughorn's class.
Corrected entry: When Dumbledore rises to give a speech, the gold owl on his pedestal shakes its head and then spreads its wings, which are perfectly clean. Later during the speech, the wings are shown covered in dried wax from the candles.
Corrected entry: When Harry drinks the Felix Felicis, he appears to drink/down the entire bottle, but the next shot shows that it is still half full. They may have shot both versions because in the book Harry only drinks half and saves the rest for later.
Corrected entry: When Harry and Dumbledore go into the house where Prof. Slughorn is staying in the beginning of the movie, dragon blood drips onto Harry's head. Dumbledore touches it, but there is blood still left on Harry's head. Once Slughorn is revealed he assesses Harry, but Harry's hair is different and the blood stain is no longer on his forehead.
Corrected entry: When Harry uses the instant darkness powder on the Hogwarts Express so that he can spy on Draco, it is daytime. When everyone clears off the train when they arrive it is night outside. Hermione says "Wheres Harry?". But there must have been at least an hour between when Harry left them and Hermione asks. Why is she only asking where he his now?
Corrected entry: Near the beginning of the film, where Harry is in the train station with Dumbledore, they are talking and Dumbledore lifts his left hand which is severely burnt. Nearer the end of the film when Harry and Dumbledore find out about the Horcrux's, Dumbledore brings out from his drawer a book from the second film and a ring belonging to Tom Riddle's mother. He explains that it was difficult to get the ring, and then holds up his burnt hand, but this time it's his right hand that is severely burnt, not his left.
Corrected entry: When Ron, Hermione & Harry are sitting in the Great Hall discussing Ron's break-up with Lavendar, there is one row of tables behind Harry - one row behind Ron & Hermione - total, 3 rows of tables. When Harry leaves the Hall, there are 4 rows of tables as there should be.