I started a new world to try out the new snapshot and i am about to get some coal and a few zombies came out of a cave, no biggie right? Wrong! out of nowhere zombies are spawning from the sky! There is no stopping them! After i reloaded in the world, by the time i started taking screenshots the zombies slowly started fading away and they are gone now but i'm not sure what triggered it. The screenshots show some of the zombies attacking me as well as the zombie meat they have dropped both in my inventory and on ground. and Where the first zombies spawned in.

Deathlogs from new launcher:
48:47 [SERVER] [INFO] Pkninja16 was slain by Zombie
Client> 2013-04-25 21:48:47 [CLIENT] [INFO] [CHAT] Pkninja16 was slain by Zombie
Client> 2013-04-25 21:49:03 [SERVER] [INFO] Pkninja16 was burnt to a crisp whilst fighting Zombie
Client> 2013-04-25 21:49:03 [CLIENT] [INFO] [CHAT] Pkninja16 was burnt to a crisp whilst fighting Zombie