What I expected to happen
I would be able to create a superflat world with a custom preset.

What actually happened
I couldn't create it. My custom layers of blocks were replaced by the default dirt and bedrock layout. It won't work on any of the 1.8 snapshots. If created on an earlier version, it will work normally on any other version, including these snapshots.The other settings, like the ocurrence of villages, were kept.
Steps to Reproduce
1. Create a superflat world with the following setting:

2;10x7,25x35;1;village

2. Enter the world. It won't be made of wool and bedrock, as expected.