World has gone upgrades as follows:

1.7
1.8
1.8.1-pre1
1.8.1-pre2

Any higher than this (pre3 / pre4) though all nether portals start acting oddly. Players transport through the portal however end up appearing either in the overworld or the nether 2-3 blocks to the side of where the portal actually is.

This has resulted in smothering in walls, falling to death in lava, and other horrible deaths.