Trivia: Not a mistake, but another elf sighting within the movie. In the Parent's Day scene in Charlie's classroom, watch the boy sitting directly behind Charlie in the blue shirt. When Charlie walks back to his desk to retrieve his glass ball to show everyone, you can see the boy's pointed ears. Another note of interest is when Charlie says "my Dad is Santa Claus" and it cuts to a wide shot showing all of the kids, this kid is the only one not laughing.
Trivia: In the scene where Scott and Charlie are flying through a big hole in the clouds, notice the clouds themselves bear a striking resemblance to the clouds from The Neverending Story. Then look to the lower right corner and you'll see the face of the white dragon from The Neverending Story.