Super buggy textures + Cloning structures, blocks disappearing.

What I expected to happen was...:
Slimes Generating like usual
What actually happened was...:
Slimes turned into... whatever it was. Shield texture super weird.
Steps to Reproduce:
1. Open Minecraft
2. Create New World (creative, superflat, seed: Cheese Biome)
3. When Slimes Spawn in their texture is super weird, same with shield texture.

Note: first picture was when I opened an old save (1.8 something). I remember making only 1 of those towers.