ZDoom

interesting, since I had a working stair which became not working through making it an odd shape, correlation not causation I guess. thanks for the quick fix!

fixed. Actually, the shape of the sector does not matter - the bug happened when the lowest numbered line to a sector with the alternative stair special is the initial sector where the stair building started. This was not properly flagged as having been processed.

It seems there's an issue with Hexen style stairs where certain sector shapes will break them, causing only the first 2 steps to be lowered.
I noticed this issue in MAP04 of GERMS V1F (viewtopic.php?f=42&t=65498), and was frustrated enough by it that I decided to look into it.
I've only been able to reproduce this bug with sectors shaped like a trapezoid, with the smallest step being the first one.

A test map I made can be found attached with 3 demonstration stairs.
The stairs on the left have a pretty strong angle (157 degrees), But still work for some reason
The middle stairs have a more slight angle (164 degrees), But are affected by this bug
The stairs on the right are directly copy-pasted from the broken stairs I found in GERMS.

I also used my extremely limited git knowledge to try bisecting the issue and narrowed the problem commit down to commit 63fa01205f9b111c8e6b27b54fe736f834b6b807 (
- fixed potential infinite loop in Hexen-style stair builder. Jan 6
But I unfortunately am not sure what the actual root of the problem is.
Considering the fact that the first 2 stairs work fine, it seems like it might be an issue with detecting the next sector with special 26 (Hexen stairs swap between specials 26 and 27 with every sector)