artifact:dependencies ignores settings-security.xml and sends password hash to repository

I have a mirror repository configured in .m2/settings.xml, and its <server> entry uses an encrypted password in <password>, using the master password set in .m2/settings-security.xml.

I followed this guide:

http://maven.apache.org/guides/mini/guide-encryption.html

I get authentication errors every time i use

<?xml version="1.0" ?>
<settings>
    <mirrors>
        <mirror>
            <id>paytronix-public</id>
            <url>https://greylock.corp.paytronix.com/nexus/content/groups/public</url>
            <mirrorOf>*</mirrorOf>
        </mirror>
    </mirrors>
    <servers>
        <server>
            <id>paytronix-public</id>
            <username>rmellgren</username>
<!-- <password> element omitted -->
        </server>
    </servers>
</settings>

I switched to http and then used tcpdump to watch the request, then decoded the Authorization header. The

password hash was sent not the decrypted password.

Looking into maven-ant-tasks.jar, I see a META-INF/plexus/components.xml which does not include plexus-sec-dispatcher from maven-core. I tried spinning my own copy of maven-ant-tasks with the appropriate component for plexus-sec-dispatcher added, but it didn't work, so I think I'm out of my depth in the troubleshooting/rectification department.