The bug

Mineshaft support legs can generate in lava, which makes no sense since they are made out of wood. In such cases mine shafts should generate support chains instead of support legs.

How to reproduce

World type: Single Biome; Lush Caves
Seed: 5318492750448728086
Coordinates: /execute in minecraft:overworld run tp @s 12.44 -50.00 -279.77 144.45 15.90