Thank you very much mrheat and Jon Chalmes! I've got this bug since 1.2.5 and I was waiting for a fix... But today I've said it's enough... I hope the people of mojang can resolve this bug for the next snapshot or update. Thank you very much! I never thought that mojang will fix a bug in my world, it's just amazing!
So is it a general bug from the game or it just happens in my world...? Maybe if I rebuild the cage, the bug fixes itself...
No, i throw eggs on the floor (the grass), and then all the chickens go to the iron bars (just one or two chickens stays at the middle...), and when all of them has grown up, they start to go through the walls... this happens since 1.2.5 version, not before. As you can see in the screenshot, there is one chicken trying to escape. If the chicken keeps in his trying to get freedom, it will be free and it happens with all of them.
I think that is not resolved... My chickens still can scape from the box... And i'm running in 1.4.7!