toggling tree expands/collapses unrelated subgroups

[valentin-pinkau]

The new feature of collapsing subtrees introduced a bug.
Activating subgroups expands or collapses other subgroups.
First bug:
Reproduce: root expand all; click on any tree -> all subgroups collapse
Second bug:
Reproduce: root collapse all; click on any tree -> all subgroups expand

[hotzenklotz]

@MichaelBuessemeyer Did you already start with this one? Otherwise I might take a look at it.

[MichaelBuessemeyer]

@hotzenklotz I did some follow-up work on the add-collapse-all-groups branch for the pr #4143. But this is not related to the issue/bug.

I also shortly tried to find the bug but did not succeed. If you want you can take a look at it.

[hotzenklotz]

@MichaelBuessemeyer I have fixed the bug in PR #4178 but nothing more. No usability improvements or other feedback. Just the bug reported here. Feel free to include these other changes as well.