darktable exporting parts of hierarchical tags

dt 4.2.1 via opensuse debian 11 repo.

There were some unexpected tags in exported files, so I investigated.

hello|world
yuppie
    duuh

Import that file as a tag list, then the overall list contains the following entries:

hello|world
yuppie
yuppie|duuh

When I assign both “hello|world” and “yuppie|duuh” to an image the exported image contains “world, yuppie, duuh” in the keywords. I would not expect “yuppie” to be in there.

My export setting is

[x] EXIF data
[x] metadata
[ ] geo tags
[x] tags
    [ ] private tags
    [ ] synonyms
    [x] omit hierarchy
[ ] hierarchical tags
[ ] develop history

The culprit seems to be that free-floating “yuppie” tag. It is not assigned to any image, but it gets exported. When I delete it, which does not change the tag list of the image, it is gone from the export.

Was that always the case?
Is that a bug, unintended behaviour or a feature?

For me it makes re-imports of taglists dangerous because they have to be cleaned up externally before they are safe to import without causing side-effects.

And it makes “growing” hierarchies impossible, because as soon as there is a tag that spans part of the hierarchy of another tag, that “parent” hierarchy always gets exported, too. Even if the options tell a different story.