Put the summary of the bug you're having here

I thought, and I've done this little combonation before and it never failed or glitched out, but this time it utterly failed. I would normaly expect the shafts to spawn like they would underground, but now they are spawning with entire areas missing of wood, but the chests or rails will still be floating there. Strange part is not even that, but if you fly up to one of the chests, you'll get hung up on air and get stopped by the bloody air it seems like.

Steps to Reproduce:
1. Generate a new world, superflat custom ( exact seed for the custom : 2;7,30x1,5x3,2;3;stronghold,biome_1,decoration,dungeon,mineshaft )
2. Get up and fly to the nearest visable mineshaft
3. Try to fly to one of the floating chests or rails, you should wind up getting stuck on invisable wood planks.