Enderdragon is Still Moving with /summon command

So I was testing things in my world with /summon and I did the wither, zombies, creepers and more, Then I did the enderdragon and The Enderdragon was moving and was not staying frozen. I also Noticed that the Dragon was getting further the more time it was there. When 1.9 First came out the /summon enderdragon command frozen the dragon.