You deleted one world, then created a new world with that same name. When you delete a world from within Minecraft's UI, there are small bits and pieces that don't get removed until you exit Minecraft, navigate to your .minecraft folder, and delete them manually. If you fail to do this, the next time you create a new world using this name it will incorporate these chunks into your new map.
Okay, thanks for explaining. I guess from now on I am going to delete my world's manually so this doesn't happen again.