World got destroyed when updating

When I updated my server to 1.7.9 from 1.7.4, in my world, biomes re-spawned on top of the plains biome my town was in, destroying the world. The houses would just be "cut out" and there would be like a snow biome there. Or like in my restaraunt a new plains biome spawned there, so it was as if I just had started the buildings. Is that supposed to happen? I don't have a screeenshot by the way... Also, in 1.7.4 once on my other computer, I generated a new singleplayer world, then next time I got on it, a forest biome spawned in a mountain, so it looked as if somebody had just cut a perfectly rectangular hole in the mountain! I was in a plains biome on the sever and an Ice Plains Spikes biome in the single player world. I don't have any screenshots. Sorry.