Please help. This has never happened to me before but twice over the last few days. The (first picture) is the world which it is happening on. The (second two pictures) is when it happened the other day. Then I deleted it, (about a months work) and had to bring in a backup which I had made on Jan the 1st. Then I just played it all last night it was fine and then today this happened (the remaining pics) again.

Why is this happening? please help me. My other worlds seem fine it is only happening to this world. The only thing I have installed is the latest version of optifine which has never been a problem. And yes I have installed it correctly, it is very easy to install and has never caused me any problems...

Is this a bug for 1.4.7?? Is it common? And please tell me my world isnt corrupted!

Also what should I do I need to record a lets play episode today on one of my other worlds, can I still do it or will i have to delete them, a backup etc. or something?

Also I have been playing minecraft for about a year and this has never happened...