Sometimes arrows appear to bounce off of entities as if they were holding a shield, even though they aren't or can't even hold a shield (example: bats). A short while later, the arrows get updated to their correct location.

Seems to happen (more often?) when the arrow barely misses, so it bounces off client-side, but flies through (or past) server-side.

To test: Summon a lot of bats in a closed room, shoot them and watch the arrows.