Concrete walls cause rust stains on wallpaper; new construction;

Here once again the full version:

https://www.hausbau-forum.de/threads/rost-an-tepete-unter-tapete-betonscheibe-neubau-mit-bildern.38032/

Painting over is useless. They will come back.

Remove the wallpaper, sand down the surfaces. Fill, new wallpaper.

What is wrong with my statement?

Your long comment is not consistent. Why expose the reinforcing steel if it is not the cause. Please stay on topic.

Why are you quoting a post that has nothing to do with my statement?
Furthermore, the long text is a discussion that offers the questioner some help, since my conclusion is only an idea, but of course I cannot promise 100% because I don't see it live.
We can leave it at that :)

We can leave it at that for both of us :)

In post #7, however, it sounded a bit different. ;)

That's true ;) because the same topic creator had another one, therefore just the short version... we get along again