I created a new survival world and entered. It was a default world type, with gamemode survival, cheats on, and bonus chest on.

I explored a bit and found giant yellow patches centered around a tiny shadow,
and it was a chicken that had rendered at 16x normal size (Also, only the yellow areas of the model were showing)

This also happened with squid. Interestingly, it did not occur with cows, and I have not tested any additional mobs.

I am running freshly downloaded clean Minecraft 1.8.
I have a resource pack, but I removed it and it isn't the problem.

How to reproduce:
1. I assume this is a rendering bug, I did not interact with the world other than destroying 2 torches and a chest before I noticed the bug occuring.

I tried reloading the world and that did not solve the problem.

Attached is the save where I noticed this occuring.