Parent: MC-156088
The bug
I went to reload resource pack and got a really weird image for one frame near the end of the loading bar. The textures seem to have gotten messed up and attached to the wrong blocks. Grass turned into green glazed terracotta and stone turned into blue. I don't even know what the scaffolding turned into. It returns to normal once the Mojang logo is gone.
Entities (including pantings) don't seem to be affected by this. Item textures are also able to be loaded by this bug.
It seems to happen more often when a texture is changed.

How to reproduce

1. Get a texture pack
2. Enter a world
3. Change any file name in the texture pack
4. Press F3+T and watch closely
5. Near the end you'll see the textures glitch for a frame