Deliberate mistake: The balloon llama the chipmunk makes has legs which are completely detached. The pairs of legs should be twisted together. Without this, it looks like the balloon has 6 different ends.
Deliberate mistake: When Alex is in the cabin opening the can the pull tab is already lifted up making it easier to open because he is wearing gloves. It was already up when he took the wrapper off.
Deliberate mistake: Some of the text in this movie is in English, but some is in Japanese. Most noticeable when Tai writes the letter to Sora.