Ender crystals not respawning when respawning a dragon

Put the summary of the bug you're having here

I made a creeper face with clay.

What I expected to happen was the ender Dragon would respawn and the crystals to reappear.

What actually happened was...:
The ender Dragon spawned, but no Crystals

Steps to Reproduce:
1. Open 15w33b
2. ...go to the end
3. ... make creeper face with clay.