Mineshaft chains can generate without a fence post when there is another fence post on a layer below it

The bug

Mineshaft chains can generate without a fence post connecting it to the wood, if there is another fence post connected to a chain directly below it.

Seed: -8131653949012933360
Coordinates: /execute in minecraft:overworld run tp @s -250.70 -30.62 -497.02 858.99 12.50