BuddyPress.org

To whom it may concern: I solved the issue by manipulating (not deleting) the doubled DB entry. In the wp_bp_groups_members table, I manually set both the group_id and user_id fields to high values that have no corresponding real equivalents (group, user). Think this now orphaned row won’t do any harm and as far as I can see, the searches like “groups of this user” or “users of this group” result in what I want now.