Hostile mobs are spawning on my command block circuits.

What I expected to happen was...:
In past versions I have not had to light my command blocks. Mobs couldn't spawn on them

What actually happened was...:
I updated to the snapshot and all of a sudden all my command blocks were covered in hostile mobs!

Steps to Reproduce:
1. Create a superflat world that is made entirely out of bedrock.
2. Set the time to night.
3. Place down some command blocks.
4. Move at least 25 blocks away from the command blocks.
5. Mobs should start spawning on them.