Mineshaft halls generating on top of each other fail to properly generate plank floor, causing rails to float

Can confirm in 1.17.1

Can confirm in 21w41a.

Can confirm in 21w43a

Can confirm in 21w44a

Can confirm this in 1.18 Pre-release 4.

Here are some extra details regarding this problem.

The Bug:

Rails in mineshafts can occasionally generate floating as a result of interesting structures.

Steps to Reproduce:

• Generate a world with the following seed and teleport to the following coordinates.

Version: 1.18 Pre-release 4
Seed: 2671478887814226195
Coordinates: /execute in minecraft:overworld run tp @s 8913.70 -20.39 -375.20 145.03 49.63

• Take note as to whether or not rails in mineshafts can occasionally generate floating.

Observed Behavior:

Rails in mineshafts can occasionally generate floating as a result of interesting structures.

Expected Behavior:

Rails in mineshafts would not be able to generate floating.

Pretty sure this bug has always been there. It's a side effect of world generation not causing block updates. Same reason caves that cut too close to rivers or oceans can sometimes expose the side of a water block without causing it to flow.