Enderdragon not remembering its health

When I was fighting the Enderdragon in a Sigle player world with LAN turned on but no other player in the world, the crystals were blown and the dragon was at about half health, then I logged out/saved and quit the world while still in the End, when I rejoined the Dragon was at full health again, I tried this a second time and it happened again. (Note: The crystals WERE blown)