I created 2 DEFAULT worlds with the seed "LightChase", one in Version 1.3.2 and the other 1.4.2 Pre-release. Both versions give me the same world with a partly generated cave (See Picture 1 and 3), a river that didn't float down (See Picture 2) at where it should be, ork trees and a lake south-eastwards (See Picture 4). I tried to recreate it several times and I was given the same result.

Then, I created a Large BIOMES world with the same seed in 1.4.2 Pre-release. This time, I was given a world with a similar cave yet fully generated (See Picture 6, notice the trees are gone), a Swamp biome which didn't show up in the Default world (See Picture 6, on the right), the same lake at the same position of the Default-world lake (See Picture 5).

I think, and I believe, that it's a generation bug occured because of a code error.