The Ender Dragon does not attack any monsters that damage it.

 Ender dragon wouldn't attack Wither, no matter how many times Wither fired grenades, the Ender Dragon didn't take any damage from Wither. Also, Wither can't inflict damage to the Ender Dragon.I think this is probably a bug that has been around for a long time because the Ender Dragon should attack Wither when it damages it, then it should be able to damage it. Can put Ender Dragon