Weird terrain bug

I created a new world to try the 3D resource pack. I saw it was causing too much lag for my nooby acer, so I turned it off, and put the chunk loading distance to 6. I returned to the game, and this happened. I quit the level and played it again, but it dind't do anything (The screenshot is after quitting and playing again). Strangely the other places around were not affected.

(edit) I found another affected place right next to the previous one, screenshots included