http://www.virtualmin.com/forums/message-view?message_id=4659
In this post, Andrew notes that Virtualmin is giving users the name of the Unix user as the "domain" component of a "user.domain" username. When the user doesn't match the domain name things act funny. I haven't confirmed this in the latest version yet but will if you don't get to it first.
Status:
Closed (fixed)