Hrm, so it sounds like you tried changing the second Virtual Server’s username from the default while creating it? Normally, I’d have expected that would get it to use a different MySQL username.
If not, you may have stumbled across a bug
If you tried changing the second Virtual Server’s administrator username – you may want to file a bug report then, using the Support link above.
Created the first virtual server flensburgersport.dk, but changed the username, and the database name to flensburgersportdk
After creating the first virtual server I did the following EDIT Databases -> Usernames -> Change Database Username -> Change to : fbsportde (I seems that Flensburgersportde was to long a username for MySQL).
Create next virtual sever and again using new names.