Cave generation is different from old generation

The bug

If you generate a new world with the same seed in the versions 1.12.2, only the overall terrain seems to be the same. Caves generate entirely different. That affects the nether as well, in fact the nether seems to use the same generator as the overworld now.

This is seed 1 looking up from 0 0 0 in 1.12.2

This is the same seed in 18w06a: