I think the picture speaks for itself, but I should probably mention that this was on 1.18.2 as I haven't had much success at getting modded minecraft to launch at later versions.

That's not a bug; I never coded that specific case. I'll consider it as a future addition but given how complex the blockstate logic already can be it won't be a simple job. In the meantime, there is a screenshot on the curseforge page that shows all the additional stair placement shapes.

Yeah, I'd seen that - I was more thinking of it being a bug in that one logical (but somewhat obscure) interaction and its mirrors/rotations had been missed in a system that accounted for literally every other logical interaction (I checked), and wanted to make sure that it was known by the author.

I'm not going to close this issue, in the hopes that it will get added in the future, but I can understand why it might not be something that can be added on a whim.

Well I ended up doing it anyways, expect it in the next release.
marking fixed as of:
b5e4f7e
540a766
bee8473