What is supposed to happen when I click on a headline in backlinks?

I have a setup where I write down notes on book I’m reading, just in one file for the book.
Now I introduced a context note like “psychology” and inside my book notes which is
structured with the headlines I then make links to this context note. So now I opened my psychology note and I see the 5 backlinks:

Problem now is:

  • If I click on a headline like *** Die ersten Kapitel in the right window nothing happens
  • If I click on the headline *** Mathematik und Statistik I get the error “Cannot make side window the only window”.

In general it looks like his error message always appears if under a headline there are several links of which just one is the “backlink”.

If I google for that error message it looks like it can come from Helm, but I’m not sure.

So what is the supposed behaviour that should happen if I click on a headline in the backlinks window? I would expect then the note to open and point placed on that headline, but that doesn’t work.