Nether Portal Crash

When ever I am near a functioning Nether Portal, my game crashes. This happens in both single player and LAN, and I first noticed it in LAN. This bug is also present with and without texture packs.

Whenever I do manage to log back in to the game, it basically functions normally until I do something such as opening the menu, jumping, sprinting, etc., at which point it freezes and I am forced to restart the game.