Disconnecting then Relogging into a world fully heals the Ender Dragon

I was fighting the Ender Dragon, and logged out so that an Enderman that I accidentally aggro'd would stop attacking me, and when I did the Ender Dragon apparently healed all the way. Tested it out in a creative world and confirmed that this is the case. This is extremely frustrating, and I don't remember this being the case in previous versions.