In previous versions, using caves generation for buffet, where lava lakes would be in the nether were replaced with water lakes. Also, there would be no netherrack in the overworld just the biome appropriate blocks.
Steps
Create New World
More World Options...
World Type: Caves
Customize
Biome: Plains
Expected
Large lakes at y=32 would be water
"underground" blocks would be stone variants, dirt, gravel, etc (based on biome selected)
Actual
Large lakes at y=32 would be water
"underground" blocks are all netherrack
Thank you for your report!
However, this issue is a Duplicate of MC-184644.
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