If you create a map under Superflat Tunneler's Dream under one name in creative with the bonush chest option on, then delete it, then create a normal survival map under the same name regardless if the the bonus chest is on or not, chunks from the supperflat world appear.

Watch the video I made to get a better understanding of the issue, and then try it yourselves.

http://www.youtube.com/watch?v=j5lLYUZZZxo