Using /kill on the Ender Dragon doesn't end the fight

EnderDragon health bar is still viewable when EnderDragon is killed using command /kill @e.

What I expected to happen:
The EnderDragon health bar is gone when the EnderDragon is killed using commands.

What happened:
The EnderDragon health bar is still on top of the screen with its previous health.

Steps to reproduce:

1. Go to End / Spawn an Ender Dragon.
2. Type /kill @e.
3. The bug is reproduced.