In an amplified world in the latest pre-release, you can find large areas where the cave biomes are open on the surface. Not a major bug by itself but it also causes the surface dirt and grass blocks to generate underground at -43, which is more of a concern. 

how to recreate:

seed: 8573426165710340175

co-ords x= -198, z= 502

the large area of surface dripstone is on the surface

the dirt is directly below at y=-43