They were fixed a few snapshots ago. My wife found a new, good lookin' shaft in her world and had me explore it while she was feeding the baby. It was nice, but it seemed to be a lot more confusing to me. The solid plank walkways make me assume that I was walking on the support beams of a shaft below me but I wasn't.
Also I think chests are more rare in the new ones; I only found three or four chests in her world, but in the mineshaft I am living in on my world I found seven or eight, plus three cave spider spawners, a skeleton spawner, and a nearby zombie spawner.