In this movie, when Jim gets an apple pie, there's a note near it that says, "Apple-you're favorite!!!" Grammar lessons, anyone? It's YOUR, not YOU"RE!!!
If you listen to the director commentary on the DVD, at that part, he mentions that it was intentional, being a character flaw (Jim's mother) instead of someone from the crew.
Actually, The Director said it would have been too expensive to re-take the scene with the correct spelling, They noticed the mistake so it's not technically a slip-up.
Just because they noticed their mistake, doesn't mean it's not a slip-up. People, stop sticking up for the movie people, if they make a mistake, so what? This site is to report mistakes, not to defend them.