If a Superflat Preset Code is used that generates an open layer (of air, a dozen or so blocks high) directly underneath a layer of solid non-transparent blocks going up to the max World Height, AND have the code generate villages, the world would fail to load at all (or just take FAR more time to load than I have the patience for).

(Discovered originally in Creative mode, but (I think) the bug can occur in Survival mode as well. I first found this bug around 12w40a, and every now and then, was able to reproduce it in several later versions.)

How To Reproduce:

1)Enter a Superflat Preset Code that fulfills the above details.

Example Code: 2;7,59x1,3x3,2,180x0,12x7;1;biome_1,village(distance=0 size=1),decoration,lake

2)Try to generate that world.

3)The final result should be either the world doesn't load, takes exceedingly long to load, or you (the person reproducing this bug) run out of patience.