Black spots

Put the summary of the bug you're having here

What I expected to happen was...:
I thought the black spots were filled in with regular ones (e.g. Stone, wood, grass, etc).

What actually happened was...:
When I walk around the world in survival or in creative, I sometimes see some random blocks that have black spots. Then, I have to put a block on the black spot for the black to disappear.

Steps to Reproduce:
1. Walk randomly around the world you are in.
2. Look at the big cracks that lead you to underground.
3. Look at the walls.
4. You will sometimes notice black spots.