I tested this and got the same thing you did. As soon as I tried to do anything on the open part of the build, the stair to the ground jumped up to the height of the platform. I also noticed that when I went to place those stairs, I tried next to the wall, and they wouldn't place. I had to move out a tile and use the stair arrows to extend the stair. The first time, I placed the platform first and then the stairs. I also tried placing the stairs first then the platform. That time the stairs jumped up immediately. So, it looks like the platform and stairs are not getting along in that configuration. I'm not sure that it's a bug and not just a quirk of the build system. Nor do I remember it happening before though so can't rule it being a bug out. Either way, I agree with you that it shouldn't happen.
Hope this helps.
The fact it happens no matter what you modify on a lot is really a big issue I think, as I'm sharing lots, I know that some people might modify some stuff and won't see the mistake. It's not that hard to solve, but the fact it happens any time you do it is really frustrating :'(
Let me guess: if an issue is getting lost at the bottom of those bug reports, it means it will never be solved ?
This one is easy to reproduce, and it's still there after the last patch.
I know there are more important fishes to solve, but it would really help not having to replace every stair when I modify something on my lot.
Thanks in advance.
