Frozen Wonderland
Elsa flees her home and sister in the animated film Frozen, determined to find a place where she can be herself. After she tosses her tiara and lets her hair down at the end of the movie’s extremely popular song, she makes this error. Her braided hair reaches all the way to her shoulder.
In the above takes, you can see the error. Mistakes like this are more unusual in animation than in live-action films, yet they do happen!