The light value is 0 when on top of a stair block

What I expected to happen was...:
When the player is on top of a slab block the sky/block light value shouldn't be 0.

What actually happened was...:
The light value is 0 during both night/day and with/without a light source block near the player.

Steps to Reproduce:
1. Place a slab block on the ground.
2. The player must be on top of the block (the y value has a .5, for example Y=66.5)