How to filter people unconfirmed, unknown or ignored?

digKam has a filter section. I can filter by “real” people tags, but when I select one or more of these artificial tags (unconfirmed, unknown and ignored)


Then nothing is filtered. The result is empty.

Is it a bug?
If not a bug: when these tags are listed, why they have no effect?

And how to filter pictures by these specific tags?