Hi, it's me again! Just wanted to say, that when you logged in in a world with 1.8, you should not ever log in into it with an older version. After dinnerbone rewrote the inventory things, he made it so that 1.8 converts it from 1.7. 1.7 doesn't convert it from 1.8 though, obviously. So when you have played a world in 1.8 in 1.7 every chest, inventory et cetera will be empty.
My little brother lost his world (well, deleted it because all items were gone) due to this, so I'm just posting this to make sure you know it, and don't do it without thinking.