World generation issue

When I was going to report a different bug, I created a world to prove that this bug existed, but I came across a much different bug.

When I created this world, I had the settings like so:

Name: Bug testing
Type: Superflat
Seed: None
Gamemode: Creative
Cheats: Yes

So when I generate the world, I get a group of chunks around the spawn that are default world type. I HAVE NO MODS INSTALLED ON MY MINECRAFT CLIENT!!!