The Enderdragon doesn't flee when hit with arrows

What I expected to happen was...:
-When I hit the Enderdragon, it will turn around and flee.

What actually happened was...:
-It continued to charge me.

Steps to Reproduce:
1. Wait for the Enderdragon to charge at you.
2. Fire a arrow at it.
3. Notice that it continues to charge you rather then run away.