Enderdragon flying through the obisidian pillars

Enderdragon flying through the obsidian pillars

What I expected to happen was...:
It should fly arround the pillars and crash if they fly into them.

What actually happened was...:
It flew right through them like there was nothing there.

Steps to Reproduce:
1. Go to the end.
2. Fight the Ender Dragon
3. Try to get the Ender Dragon to fly through the pillars.