if you will check our guide at http://www.psoft.net/HSdocumentation/user/mailing_lists.html you will find:
As per ezmlm manpages, "there is no reason to combine of SENDER checks on posts with message moderation. Therefore, the combination of the -u switch with the -m switch is used for a configuration with SENDER restrictions (like with -u alone), with the difference that posts from non-subscribers will be sent for moderation instead of being rejected. This allows the list admin to let non-subscribers post occasionally, as well as to catch subscribers posting from non-subscriber addresses."
That's why mail from the subscribers is not moderated.
Mail from the users that are not in the subscribers list is moderated.
You should choose only one of these features.