Hoppers will show their breaking animation on the top part despite nothing being there in the texture.
Steps to Reproduce:
1. Make a new Creative world.
2. Give yourself a stack of Hoppers and a Wooden Pickaxe.
3. Switch your gamemode to Survival, place a Hopper, and begin to break it.
4. Notice the breaking texture appears on top, though it should not.
This is related to