When you hit with a splash potion a sheep it only disappears the face but not the body

When you hit with a splash potion a sheep it only disappears the face but not the body

What I expected to happen was...:
What i expected to happen was that the sheep disappeared completely..

What actually happened was...:
What actually happened was that it only dissapeared the face.

Steps to Reproduce:
1. Find a sheep
2. hit it with a splash potion
3. Watch it