If i create a mysql user as add mail/fpt user then we have a problem.
We use the domain.username formula, in this case virtualmin add the domain prefix before the user name.
(we prefer if virtualmin can add the whole domain name to the user names but it's an other issue i think. may i open a new ticket for that?)
So the problem is mysql has an username length limit (default 16) and the insert truncate the end of the username (yes we can incrase the username length as mysqladmin so that's could be ok - this is why severity very low)
But i suggest to validate the username length from virtualadmin to avoid later problems like this:
http://www.sitecrafting.com/blog/mysql-login-truncation/
like:
verylongdomain.verylongusernameone will be
verylongdomain.verylongus
and
verylongdomain.verylongusernametwo will be
verylongdomain.verylongus
so they will be the same mysql user -> exactly grant more privileges to the frist one.
We host domainnames with more then 30 characters so that caused some problems :)