The Bug:

Mineshaft can override itself or another mineshaft, causing wonky generation and issues such as: support pillars and fences floating, fences generating in invalid configurations (MC-236433), corridors being cut off and/or blocked by support pillars and fences, floating rails (MC-125343), floating pillars, et cetera.

Here is an example:

Seed: 8587948038190963789
Coordinates: /execute in minecraft:overworld run tp @s 4806.49 13.00 161.86 207.30 15.75

Steps to Reproduce:

1. Generate a world with the seed provided above and teleport to the given coordinates.
2. Look closely at the generation of the mineshaft.
3. Take note as to whether or not mineshafts can intersect themselves causing wonky generation.

Observed Behavior:

Mineshafts can intersect themselves causing wonky generation.

Expected Behavior:

Mineshafts would not be able to intersect themselves.