Subgroup Issues on board are displayed in both Backlog and their label list

Summary

When using the issue boards some issues are displayed in the Backlog list and in the own label list. It looks like only the issues from subgroups projects are concerned. Also, this only happens when filtering on milestone using the board scope. When filtering on milestone using the search/filter bar it works fine but state is not saved in the board.

See next:

Boards___duplcate_issues_in_backlog

Example Board

https://gitlab.com/groups/gitlab-org/-/boards/554644

What is the current bug behavior?

Issues are shown both in backlog and label list.

What is the expected correct behavior?

Issues are shown only in label list.

Output of checks

This bug happens on GitLab.com