I know this is 4 years later but this is due to you attacking a "zombie leader". It is a type of zombie that has a chance of spawning depending on regional difficulty on hard mode and can spawn "reinforcement zombies" to help attack. Either way, the reinforcement zombie is not supposed to target the player in creative mode so this is a valid bug.
NotAPolarBearXD
I know this is 4 years later but this is due to you attacking a "zombie leader". It is a type of zombie that has a chance of spawning depending on regional difficulty on hard mode and can spawn "reinforcement zombies" to help attack. Either way, the reinforcement zombie is not supposed to target the player in creative mode so this is a valid bug.