Hi.
I just upgraded from 1.610 to 1.680 today, and there is a bug on the home page of usermin.
line 60 of blue-theme/right.cgi is concatentating $user{'id'} before checking if it exists, which logs an error to the log file.
Simple fix:
Change $infp{'id'} to ($info{'id'} ? $info{'id'} : "")
I don't know if this has any other ramifications - it is a hidden table anyway, so I'm not sure what it is doing there...
I typically have the mailbox module blocked for users (I use roundcube, and most of my users don't have their email stored under their linux account, but a virtual user), but I tried enabling the module to see if the error would go away, and it didn't.
Thanks - this will be fixed in the next Webmin release.