I was running around in my achievement world looking for wolves to tame for the Leader of the Pack achievement and I kept seeing movement on the edges of my screen. It took me a few minutes to realize that what I was seeing were snow layers on the ground disappearing.

According to the wiki, this happens in dry biomes. I was in a cold taiga forest. That's not a dry biome. Granted, the core section of this world, where my base is, was created before the TU31 update, so before the way biomes generate was changed and the new types of stone and soil were added, but it should still be a cold biome and the snow should not be melting there.