I've been seeing this for some time now with the world generator with the new world types. This example in particular the "Caves" option. Generates in a similar fashion as the Nether dimension. It even generates netherack as the stone.
MC-187962
World Generation Issue
Resolved
Duplicate
1
Nikalis MacDougall
(Unassigned)
Unconfirmed
(Unassigned)
1.16 Pre-release 2
Retrieved
Thank you for your report!
However, we are already tracking this issue, and this report is a Duplicate of MC-184644.
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