Now in one certain world (which I play most in), the blocks are glitching. There are other glitches including the nether portal and crafting.

1. Three blocks: Gravel, furnace, and flowing water. These blocks have parts that are not part of the block. For example, the gravel is one-fourth lava on all its faces.
2. I can create stuff with things I don't have in my inventory. I can sometimes make quite a few stone slabs when I didn't have any stone.
3. Every time I try to use the nether portal, it crashes.

Sorry I can't include the screenshot.