Certain nether portals (seems to be ones built in previously generated chunks) will crash the game upon entering, but before crashing will teleport the the player to the correct location in the wrong world.  For example, entering a nether portal in the nether at location 200/50/200 will crash the game, and upon starting the game again the player will now be at 1600/50/1600 but still in the nether instead of the overworld. 

This issue does not effect all nether portals, it only seems to be ones built in already-generated chunks.  If I walk out to some new, previously ungenerated chunk and build a portal, everything will work fine.

In the attachments is the error log, I will also upload a video of it happening eventually.