It is possible to configure a "delete user from group script", using %u for user and %g for the group. When doing a "net rpc group delmem" or manipulating via NT User Manager, the operation fails and the logfile shows that the %g is replaced with the username on invocation time (instead of group name). Feb 28 16:35:50 localhost smbd[4898]: smb_delete_user_group: Running the command `/usr/bin/gpasswd -d "root" "root"' gave 1
Cannot reproduce this, sorry.