Zombies Can See Me through One Block Floors

Zombies Can See Me through One Block Floors specifically grass blocks (I don't know about any other blocks)

What I expected to happen was...:
The Zombie Would Not agro on to me

What actually happened was...:
It Could See Me and would follow me through a one block floor

Steps to Reproduce:
1. Have A floor one block thick made of grass
2. have a zombie under the floor
3. Then it will follow you