Harry Potter And The Order Of The Phoenix - Height Miscalculation
During the scene when Harry and the gang are in the Ministry of Magic, when they are in the huge room looking for a certain object. Neville looks up at a shelf above, showing a glowing orb and yells for Harry. In the next second it shows Harry, much shorter than Neville, looking directly at the orb.
Yes,I've also noticed this one :p Neville's(Matthew's)height must have caused some trouble(not a slip-up or anything):when they're all at the Ministry each being held by a different Death Eater and Bellatrix (Helena Bonham Carter) is holding Neville (right before the Order arrives) you can see that Matthew is on his knees and still about the same height as Bella (Wasn't Bellatrix supposed to be tall? Sorry if I misunderstood :))