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)
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McModknower
This also happens in 20w18a with and without Opening it to lan