Sides of copper grates visible when using waxed and not waxed versions of themselves

While messing with the trial chambers I unwaxed a grate and realized that something was wrong

What I expected to happen was...:
Sides between the waxed and unwaxed version would not be visible

What actually happened was...:
They were visible

Steps to Reproduce:
1. Put a waxed and unwaxed copper grate next to each other
2. Look through one into the side of the another

 

with the same kinds of grates this doesnt happen