I've enter the End at Realm server which was set by Mojang translation managers. The Ender Dragon was stucked on one place in the air. He did not touches anything. The health bar was not displayed and the dragon was not attacking and I was not able to kill him with normal way, so I have killed him with the /kill @e command later. Before I killed him, I spawned the another dragon by placing the End crystals around the End fountain. The new, spawned dragon was behaved normal.

Screenshots were taken with my HD texture pack, but I have turned it on after I notice the bug, so that is not the cause.