Ghasts will never become hostile to players in Creative mode if they are attacked.
Steps to Reproduce:
1. Make a new Creative World.
2. Spawn a Ghast.
3. Fly up to the Ghast and attack it.
4. Notice how the Ghast will not attempt to fight back.
Linked issues
Comments 4
From MC-3039:
...as well as all hostile mobs losing interest in you after a short period after you attack them.
Please read the linked bug report before asking questions.
Relinked to MC-15111.
Duplicate of MC-3039, please use the search function to see if your bug has already been submitted. Currently over 50% of tickets are being closed as duplicate.
Hostile mobs do not attack players in creative, as you cannot be damaged in creative mode. This is a part of their AI.