The bug I have found is when you find a village, certain blocks like the stairs on the roofs of houses, stairs entering a building, and doors are not rendering / causing the player to get stuck when passing over / through. Placing a block where they are supposed to go will cause them to reappear. However if you quit the game and reload then the blocks which weren't being rendered previously will be completely gone when you reload the game.

Steps to Reproduce:
1. Load a new world in 15w35b
2. Find a village.
3. Go to any building which is supposed to have stairs used for roofs, or any building with a door. The stairs or door will not render, but you can / will get stuck in the hitbox.
4. Place a block where the stairs / door should be, will cause them to reappear.
5. Quit the world save.
6. Load the world save again.
7. The stairs / doors in question will be completely gone this time, instead of just not rendered.

The pics below, the first is when i first encountered the village before any screwing around with, the 2nd is when i placed a block causing the stair to reappear. The third picture is after a relog where the blocks disappeared again, for good. And the final picture is another attempt at placing a block where the stair should be, and it coming up as a regular log this time rather than the stair.