(old save, fully updated, no mods)
I’m unable to place any objects in this area above the staircase, not even with ALT
That’s the floor below
Exactly where the stairs below are, I can’t place anything, right next to, it’s possible
EDIT: Placing walls is possible
I was able to 100% confirm this.
Thank you 
(You even found the same house!)
Forgot to mention in the first post: This is a prebuilt house, Hangyeol House in Dowon
So it should be easy to test for the developers.
I used the same house by accident because it was the only one I had in the save file with one of those staircases 
I ran into this problem with my Air Asri House (that I later uploaded on Canvas.
I actually had to push one of the wall on the second floor that passed in the middle of the stairs of the first floor back to be able to delete and replace said stairs (had become unusable in 0.4.0 or thereabouts), then once the stairs were re-placed, I was able to move the wall back to it’s original position, and playing with both the wall and the stairs also destroyed my sloped roof.
Some shenanigans happening for sure.
I hope they fix this… I think it happened with the hotfix where they changed some stairs (ppl complained about losing the empty space behind them).
Cross your fingers.
In some of my buildings, I had to delete the stairs under the floor so that I could place a sofa, etc., over the space where the stairs had been temporarily deleted. After that, I replaced the stairs on the lower floor. But this solution didn’t work in my last commercial building. I don’t know if it’s because of the type of property or if something has been changed by the developers again.
I wonder why this serious issue never made it in the ‘Known Issues List’ and never got an answer from a Moderator.
What are the criteria?
I get it when there’s only one person reporting sth that can’t be reproduced.
But here are several players confirming this issue and it can be reproduced easily.
This bug could even be related to the problems other players have with stories above the second floor and it might help the Devs to understand what’s going wrong.
If I remember correctly, this problem with placing objects above stairs has already been noted by the developers. I think it was even mentioned on Discord, which seems to be where the developers focus most of their feedback. That’s why I was a little bit “surprised,” since it should actually be a known bug and I assumed that it was already known. There’s just a lot that needs to be improved. The developers are willing to improve inZoi and love their work. However, given the number of suggestions on Discord, they occasionally lose track of the big picture and the main focus of bug fixing, in my humble opinion.
