NBT data recognization in /kill is glitched

Discovered this when trying to specifically kill baby zombies.

Steps to reproduce:
1. In a world with no baby zombies, do /kill @e[type=Zombie]

{IsBaby:1}

and nothing happens.
2. Spawn 2 baby zombies into your world and do /kill @e[type=Zombie]

{IsBaby:1}

again.

What comes out are 2 weird results saying "(Player) fell out of the world", and "Killed (Player)" twice. Screenshot below in attachments.