Ender Dragon Re-spawning Upon re-entering the end

So, after much hard work, I killed the ender dragon in snapshot 15w51b. To cap it all off, I blow myself up with a bed on accident. When I return to the end to get my stuff, a new ender dragon had spawned. I hadn't done any sort of ritual to respawn it, it was just already there when I went to the end again. I should mention there was also no boss bar for the shouldn't-be dragon. The dragon egg was gone but the portal was activated, so I escaped to the overworld, quit out, and wrote this post. I have no idea if the bed explosion had something to do with it respawning or not, I assume not.

What should have happened:
I expected to come to a peaceful end island and get my stuff that hadn't gotten blown up and return home without being in danger.

What actually happened:
I arrived in the end to be attacked by a new ender dragon with no boss bar that shouldn't have spawned.