I got on my world that was created in like 1.5 I guess. I usually play it on 1.7. THE FIRST TIME I GET ON THIS WORLD IN 1.8 THIS HAPPENS. I noticed when I got on that nothing was in my inventory. I immediately panicked. My signs had quotations and "null" on it. My pictures all fell off the walls. All my buildings are there. Everything in my chests and inventory are not. This is seriously the fourth time this happened to me. I just want to give up on single player now!! All my important worlds are being corrupted!!! I hate having to go to back-ups and sometimes I don't have one. I had a back up for this one, but this has to stop. I understand if you can't find the problem, but I just can't ignore this.
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I haven't done that today, but I have done that recently. I have been switching from 1.7.10 and 1.8 because a server I get on isn't updated to 1.8 and I get less lag on 1.7.10 on the server.
Thats probably why.
Did you happen to update then go back to an older version? If so that's the problem.