Yeah, as of 3.60, it creates those two domain names in the hopes of making Virtualmin/Usermin easier to access (ie, your users don’t have to remember those port numbers at the end).
You can modify how that works by going into Server Templates -> Apache Website, and then if you scroll 2/3 of the way down, you’ll see “Redirect webmail.domain to Usermin?” and “Redirect admin.domain to Virtualmin?”.
-Eric