Hello,
I am experiencing the following behavior.
I renamed a virtual server and selected the options to automatically rename the admin user, home dir and group.
After changing the domain name, the group quotas for that domain weren't matching the actual usage so I searched the entire system for files owned by that group and found that the /var/lib/mysql directory and all of its subdirectories had the group changed to the new group name for that particular domain (I guess originally it should be "mysql").
As a test, I changed again the name for that domain and lo and behold, the /var/lib/mysql directory had again the group changed recursively to the virtual domain group.
Additional information:
1) The particular virtual server has no email enabled and when changing the name I saw the following message in the printout:
. Mail for domain failed! : mysql::execute_sql_logged failed : SQL set password for [...] failed : Can't find any matching row in the user table at ../web-lib-funcs.pl line 1433.
2) Operating system Debian Linux 8 Webmin version 1.860 Virtualmin version 6.01.gpl-3