The world was generated in 49a, but I doubt anything has changed. 

Yes, it is still in 51a.

In my survival world, I found a ton of floating rails in a mineshaft. One was on a cobweb, and most were just in midair. I think it is because two mineshafts overlap in that location and causes said error. In a nearby spot, you can find some other very weirdly generated parts of the mineshaft, but they aren't rule-breaking like floating rails.

Seed: -1390181176119675330

Coords: 332 12 344