ender dragon by /kill @e

i tried the new snapshot (first time in 1.9 for me so maybe it will affect more versions) and i didnt want to kill the dragon (im lazy) so i did /kill @e and the bar didnt disappear i go to the end again search for him and hi finds me i do it again same thing but next i go in i wait 5 minutes and hes not here but bar here i spawn a new one and same thing