I was fighting to the new ender dragon.
The gamemode all time was survival under the fight.

I broke all ender crystals.
And Ender Dragon went on the end portal, took 4 breathes around of her.
and denied any of my arrow shots. (I know it is supporsed to happen.)
While this time, she blocked any of my arrow shots for protect herself.

After it...

What expected to happen :
The dragon leave from the end portal and attack me from the air.

What exactly happened :
The dragon didn't leave from the end portal and forgave my arrow shots until the death.
The dragon's motion became slower that looks like the intention of flying on the air.
When I gave her a bucket water flow, it made her's motion slower to slower.
After re-entered the world, this issue has been clear. She was flying usually.

Reproducing :

Reproduce 004(downsized raw video, no cut) MC version :15w33c
http://youtu.be/U3X8PmLevOo

Reproduce 005(raw video, no cut) MC version : 15w34b
http://youtu.be/aG_uiDYoX1I

Reproduce 005(raw video, no cut) MC version : 15w46a
https://youtu.be/Dw0EP9jcexk

The below is still not certain steps.

All time, Survival mode, no death.

1) Break all ender crystals. (I still can't reproduce at the condition that ender crystals remaining.)

2) Allow dragon's breath attacks 1 breath -> 0 breath(stay on portal only) -> 3 breathes -> 4 breathes(or 3 breathes -> 4 breaches -> 3 breathes -> 4 breathes) whilst repeating go and away to the dragon. Be close to her before she starts breath attack(it looks like can take a few delay for the player. Try to make her the delay each time) , and away from her after she started breath attack. Repeat it until it reaches breath counts each time.

3) (Recommended but looks like not related) At the 4th breath, make an arrow stucking on her by shooting.

4) If she still can leave from the end portal, Back to step 2 but allow dragon's breath attacks 3 breathes -> 4 breathes.

If you're lucky, this issue will be reproduced.