Mooshroom cow hitboxes shown on back

Mooshroom cows have what I think are hitboxes on their backs.

What I expected to happen was...:
I don't think the hitboxes are supposed to be visible.

What actually happened was...:
I had quite a lot of mooshroom cows in a pit in the ground to keep them out of the way whilst I was building something. The mooshroom cows got struck by lightning so some of them turned into brown mooshroom cows (which I didn't know could happen, I think this is such a cool feature!) The bug I am reporting is that the mooshroom cows now have what I think are the hitboxes of the mushrooms on their back visible.

Steps to Reproduce:
1. Put a lot (quite a lot!) of regular mooshroom cows and maybe 3 sheep (also, there could possibly have been a chicken or two in there somewhere) in a 10x10 hole 4 blocks deep into the floor.
2. Lightning strikes them, turning maybe half into brown mooshroom cows
3. Now the mooshroom cows have visible hitboxes on their back

 

Update: After playing a bit more, I have noticed that the same kind of hitboxes are shown around other things as well. Such as fire/smoke and carrots growing in the ground.