In Creative Mode, all-hostile mobs (Mobs that are never neutral, such as skeletons, zombies or creepers) are unresponsive, even when hit, but they immediately become aggressive if the player changes to Survival mode. However, this does not apply to Spiders or Endermen.
Duplicate of MC-15111, please use the search function to see if your bug has already been submitted. Currently over 55% of tickets are being closed as duplicate.