Changing fast graphics to fancy while inside a block will make the block render all six sides

Only works when you are inside a leaf block, e.g. riding minecart.

Steps to reproduce:
1. Place a minecart under a leaf block and ride in it, so you get your head inside it.
2. Change graphics quality from fast to fancy.

The leaf block will render all six sides, causing z-fighting with the adjacent block's textures.