I think it has to do with Herobrine...

The world I created for creative and it put me in survival. Behind me was the the Herobrine monument that most people know. I dug under it with my fist through the sandstone to see if there was anything and there was a chest with a book. It was titled The Secret. When I opened it my game crashed, and when I got it back there was nothing in that world. I had also looked for the seed for that world, but it was nothing. If you try that in your game, leaving it empty gives you a random seed.

That is unusual.