Basically, my friend opens a LAN world and port forwarded it to a server. When I joined, absolute TONS of graphical glitches happened. First, glitchy water tops started appearing in random spots at random angles, looking down. Then villagers started randomly disappearing and reappearing, along with bows appearing in front of them (invisible skeleton?) and invisible spiders appearing under them, plus randomly getting squid legs?! Then the shifting. My head went 2-3 pixels out of my hat down and back, then my head was in my back, and I was floating 1-2 pixels above the ground. I have a feeling that its something to do with the LAN world being a server. I have a video, at https://www.dropbox.com/s/rr67hwlipdidqyq/javaw%202014-06-26%2014-14-41-90.avi

Edit: Even weirder. Inventory appeared to the top left of the screen. Still on the topic of lan servers.