Deliberate mistake: When Lilo is told to think of a name for her "dog" while at the Aloha Animal Rescue, there's an adoption document on the desk. The document's paragraph is in fact an acknowledgment of appreciation for this movie's production. Although it's only briefly seen twice, there's sufficient time to read a few words, such as "project Lilo and Stitch" or "at Disney-MGM Studios," and particularly in the close-up as it's being stamped "making of Lilo and Stitch," the last words of the paragraph. (00:27:00 - 00:27:25)
Deliberate mistake: When Scrat's coconut falls from the tree, it has already had its husk removed. The directors confirm this on the DVD commentary. They may have been worried that a lot of their audience would not recognise a coconut with its husk on. (01:11:45)