Minecraft 13w19a Bug Report. Survival World Problem

Playing a Single Player, and after building a house, chests, decent tools and such, etc. I left, logged off, and then later returned and got on the single player map. When I entered, the wolves I tamed had disappeared, the chunks had reset and none of the things I destroyed nor the house was there. All I had was my inventory load-out. This happened in the last snapshot as well. And I'm not sure if it's because it's supposed to, or if it's an actual bug, but It's frustrating. Basically, all placed or destroyed blocks & entities are reset, along with any tamed animals and such.
Thank you for looking into this