Bug with worlds.

On the 22nd I deleted a world, because I accidentally created it as a not Super Flat world, called My World. I then created another world and built some amazing things that I was really proud of on it, called Delilah's World. I clicked Save and Quit to Title. But the next day, I clicked on my only world, Delilah's World, and everything had been replaced (even the items in my inventory) with what I had deleted in My World. This has happened five times now. I play on a Windows 8 Dell computer, on 1.8.7.