Audio problem: When Eric and Ariel swim to each other, she says, "Eric, you've got to get away from here." He replies, "No, I won't leave you," but his lips don't move. (Regardless of the reason, still a mistake.)
Audio problem: In the Diamond Edition Blu-ray, near the end of "Part of your world." The shot of Ariel descending and Flounder's reaction shot are reversed, making Ariel's mouth out of sync with the song.