I'm not sure if this is a bug, but the default firewall that Virtualmin sets up does not allow FTP for some reason. I used the install script to install Virtualmin. When I tried to login to FTP, it would take a while to connect, then when it did connect, I would get an error (sorry, I didn't record it). Disabling and redoing the iptables seemed to do the trick because now I am able to use FTP normally. Might be something to take a look at if this wasn't done intentionally.