Parrots become invisible when on a players shoulder while player swims up.

If a player has a parrot on their shoulders and they start swimming upwards (without being on a block first, because that simply makes the parrot leave the shoulder), the parrot remains on the player's shoulder, but becomes invisible. The parrot only becomes visible again when it leaves the player's shoulders.

Imgur link showing bug in detail since file is to large to attach:
http://imgur.com/a/wqPWE