MySQL maximum username length interferes with VMin usernames

Say I have a domain "test5.tianet.de", and create a mail user "test1", with login "test1@test5.tianet.de". When I give that user access to MySQL databases, his MySQL username gets truncated to 16 characters, here "test1@test5.tian".

VMin documentation though says:

"Allow access to databases

This field allows you to select which databases owned by this virtual server the user can also login to. [...] The user's login and password will be the same as those he would use for FTP or IMAP."

This circumstance with the 16-characters-limit (which according to the manual appears to be hardcoded in MySQL) should in my opinion taken into account in VMin, e.g. at least be documented, even better displaying a warning when giving a user with a long username access to MySQL DBs.