Nether Portals can crash the game.

Description:

When entering a nether portal the game will freeze for about 15 seconds the the game will stutter and crash. This seems rather consistent as I currently have portals that I have not been able to travel through in my world, even after many attempts. 

Steps to Reproduce: 

 Enter a nether portal and the game will crash.

Expected Results:
The game should not crash when the player try's to use a nether portal.