Put the summary of the bug you're having here

What I expected to happen was...:
I thought it would be dark under the bedrock, as in previous versions of Minecraft.

What actually happened was...:
We clearly see under the bedrock, and the slabs placed on the layer of bedrock (in creative) its light.

Steps to Reproduce:
1. Go to a flat world in creative mode.
2. Dig and look under the layer of bedrock.
3. Place a slab to blace a block of bedrock, it will be bright.