1.6.2 black hole bug

Since I have installed 1.6.2 ( I was 1.5.2 juste before ) I have a big black hole with hundred of chickens who spawn in my map ( pics 1 and 2 ) and a place where I can build but if I reconnect it's all gone ( pic 3)...
It's at the same place ( 20 blocks ) and sometimes i can't load the game here... lag
Thanks for your help