msdeploy.exe is erasing FTP permissions on a site it's been told to ignore

I'm using msdeploy.exe to duplicate our live web environment to an offsite disaster-recovery server. This offsite server also hosts an FTP site that we use for transferring database backups and logs.

By default, a full webserver sync using MSDEPLOY will remove any site on the target server that isn't on the source server, so to avoid nuking our FTP server every night, I've explicitly ignored it in the msdeploy command line.

The command line is as follows (formatted for readability)

msdeploy.exe -verb:sync 
    -source:webserver,computername=HAPPYWEB 
    -dest:webserver 
    -enableRule:DoNotDeleteRule 
    -disableRule:SkipInvalidSource 
    -skip:WebSite="FTP Backups"

In IIS7, under the "FTP Backups" site, there's a node called "FTP Authorization Rules". For the FTP site to work, I have to add an Allow entry to this section, granting read/write permissions to the appropriate users.

The msdeploy command line is completely erasing this setting - although the FTP site remains online and intact, the FTP Authorization Rules section is being wiped, which means our scheduled transfers fail until someone logs in and re-creates the appropriate rules.

Is this a known issue? Can I work around it using some setting in msdeploy? And if not, does anyone know where I file a bug report against the Web Deployment Tool?