Mineshaft generates underwater without support

Steps to Reproduce:

1. Load a world with the seed 350235726360362092;
2. Travel to the coordinates -2940, 60, -1140

Observed Results:
A mineshaft was generated completely submerged, without any supporting blocks.

Expected Results:
The mineshaft either doesn't generate at all, or creates supporting pillars.

Screenshots/Videos attached: Yes

Notes: