[MM3-users] Mailing lists sometimes do not honor moderation_action of non-members

We notice that sometimes mailing lists do not honor moderation_action of non-members. Instead, it follows the default action of the lists. It looks like we can sometimes fix the issue by adding/removing the non-members or adding/removing them as owner in certain order but we are not sure about exactly what we have to do. So, it looks like that it is not caused by the list configuration. We have already verified from the web UI, mailman client and the DB table member that moderation_action of the corresponding non-members are set correctly. Any clues for us to provide further information to troubleshoot the issue and any recommended workaround to get around the issue? Thanks a lot.