Continuity mistake: As Buddy walks out into the street at the start of the movie when the cat is playing dead, you can see several parked cars on the street behind him. When the van backs up to 'catnap' buddy, there are no parked cars. Then as the van drives off again, there is a different bunch of parked cars in the street. (00:03:54)
Visible crew/equipment: During the Quidditch match Harry's broomstick tries to shake him off, due to the spell. After Hermione tells Ron, "Leave it to me," in Harry's last close-up before he flips over, the seat that is attached to the broomstick, to make it more comfortable for Dan Radcliffe to sit on, is entirely visible. Glimpses of other seats can be had during the match as well. (01:20:50)Super Grover
Continuity mistake: In the beginning scenes, where Milo Thatch is practising his proposal, he slides over (face forward, chest against the board) a chalk drawing of a map detailing the location of Atlantis. When he realises he wiped off the drawing, and sees it on his clothes, he stands in front of the blank part of the chalkboard, "filling in" the space with the map that rubbed off on his shirt - the only problem is, that the image should have rubbed off backwards as he was facing the board when it transferred to his clothes. He could not simply stand in the place of the missing map face forward and have it read properly.
Other mistake: In the beginning, the girls arrive at the airport in Chicago and you can see a billboard in the background. Then the credits roll and they land in the sunny Bahamas and as they are driving away in the limo, the same billboard can be seen in the background. Guess they were on a tight budget and had to computer generate the snow over a scene filmed in the Bahamas.
Continuity mistake: When Mario walks out of the bus station to meet his auntie and cousin, he is holding 3 bags. 2 rucksacks and a sports bag. The sports bag is all black. When he arrives at his auntie's house, he takes his bags out of the trunk. The 2 rucksacks are the same, but the sports bag has gone from all black, to red and green. (00:45:10)