The music note hanging in Blaine's locker is backwards for most of the time it's visible while Kurt is thinking about Whitney songs, but at the last second before Blaine closes the locker, is flipped and hanging the correct way.
In the "I Want to Dance With Somebody" number, both Santana's and Brittany's costumes alternate between Cheerios uniforms and green dresses. Their hair also changes between ponytails and styled.