I took a look at this in a test build and got the same thing to happen. The error I got when I tried placing the stairs was Incompatible with Terrain Constraint Block. Ladders worked fine but stairs wouldn't. So I agree with you that it is either a bug or a design oversight since it does work if the first level is flat to the ground. It should work if the foundation is raised too.
What I found really odd was that I could place a stair from the basement that ran through the hole in the floor to the 2nd level above the basement but not from the basement to the 1st level. So I can build a 2 story stair but not a 1 story stair from the basement.
Hope this helps.
@crinrict I've seen that post when I was scouring the forum for a post on this issue - I'd have added my reply to one instead of creating a new post.
Looking at that post closer, it seems like two parts of one big combined issue.
1) if you have a ceiling on a basement, you can't create a "balcony" overlooking the basement and the issue that OP in the other thread posted happens: placing stairs will cause the surrounding terrain to raise as they've shown.
2) If you remove the ceiling to create a "balcony" overlooking the basement, you can't place stairs leading up to the ground floor at all. You can still place a ladder to the ground floor, or as CGrant54 tested, a staircase all the way from the basement to a first floor though.
This is a demonstration of the possible staircase and ladder placements - after removing the basement ceiling to allow for a balcony overlook. The only thing that's not possible: a staircase directly between basement and ground floor within that open space. If the basement ceiling is present, the issue in the other post happens.
I think maybe you can merge the posts because they're related. Bottom line is: right now, the bug/issue/hopefully not feature is that you can't have balcony overlooks into a basement without something not working right.
