biome bug; Re neather

-survival game started in 1.6.2
-new update biomes loading no problem when new chunks load

• but
  -when I entered neather portal in original spawn location
  -moved distance in neather and created a second nether portal to exit
  -re entered overworld from second portal
  -using compass, made way back to spawn (distance of 1 MC day)
  -arrived back at spawn and a new biome had taken over the area like original had never existed