Two Ender Dragons?

My first 1.9 Snapshot test world acted a little weird, so I created another one. I then went to the end, to find 2 Ender Dragons. I killed the first one, and the portal to the other islands didn't come up. Once I killed the second one, the portal appeared. I'm not sure what could have triggered this, or if randomly, 2 Dragons spawn in random worlds. I did kill the two Dragons before I could get a screenshot, so I recreated the world and went to the end again. Although, there was only 1 Dragon again.