Other mistake: When Harry is talking with Arthur Weasley at the Leaky Cauldron, the number '301' (colored in white) digitally pops up right underneath the wanted poster. The composite people neglected to remove it. This mistake occurs in a DVD widescreen version, and not visible in all versions. (This is not referring to Sirius Black's number '390' written on the paper that Sirius holds in the poster). (00:16:50)
Other mistake: When Arthur takes Harry aside at the Leaky Cauldron, the moment before Arthur says, "There are some within the Ministry who would strongly discourage me from divulging what I'm about to reveal..." we can see the digital number "300" flash on the stone pillar to the right of the wanted poster. (This occurs only in the fullscreen version, as opposed to a widescreen version where the number "301" flashes underneath the poster, which is noted in another mistake). (00:17:30)
Other mistake: Right before Ron pushes Harry towards Buckbeak, you can see him glance to the right several times, as if waiting for a cue. (00:32:40)
Other mistake: On the Dutch edition of the POA DVD, you can choose either English or Dutch audio. During Snape's werewolf lesson, he demands the students to "turn to page 394". On the Dutch audio version Snape demands "page 349" (considering the way in which the Dutch pronounce numbers an understandable mistake, but still a mistake), and it occurs each time Snape demands for this page. However, the Dutch subtitles oddly enough get the correct translation of the page number. (00:49:35)
Other mistake: When Harry gets the map from Fred and George, he watches it and then one of the twins taps it and the contents fade away. But the text to the left, in shadow of the folded pages, doesn't fade. (00:58:15)
Other mistake: While Hermione and Ron watch, cloaked Harry starts up with Malfoy and his two friends as they all stand in the snow. Most noticeable in the wide shot, when Harry spins the Slytherin boy, although the boy's feet visibly disturb the snow, Harry's feet do not make a mark - no footprints whatsoever. (01:02:30)
Other mistake: When Harry and Hermione travel back in time with the Time Turner, Hermione states that the time is 7:30, we then see them run to Hagrid's shack. As the camera passes through the clock on the castle, it shows the time is either 2:00 or 12:10. As well as this we are told that Buckbeak is to be executed at sundown, but he is executed in broad daylight, looking more like midday. (01:43:40)
Other mistake: After receiving the new Firebolt Harry runs outside to use it. In the close-up as he takes off and in the next wide shot many of the students' eyes are not in sync with Harry's flight. (02:09:15)
Other mistake: When Fred and George pass on the Marauder's Map to Harry, we see the map start to reveal itself. As it does Harry starts to read "Messrs Mooney, Wormtail, Padfoot and Prongs." Harry reads the word Messrs before it even appears on the page.
Other mistake: During the whomping willow scene, Hermione does indeed say Rupert, not Ron. She says it quickly, but I am not the only one who hears her say Rupert. She definitely does say Rupert. I just listened to it 3 times to make sure. [This may differ between versions - people are equally convinced on both sides.]
Other mistake: When Lupin is teaching his class the spell to disarm boggarts, he tells them the pronunciation is "Riddikulus." When Ron steps up for his first practice, he says "Ridiculous," so the spell shouldn't work for him.
Chosen answer: Fred and George used the map to aid them in their mischievous activities at Hogwarts, and probably had little interest in what their little brother was doing or who he might be with at any given time.
raywest ★