Passwords problems

I’m running this system:

Operating system Ubuntu Linux 10.04.2
Webmin version 1.570
Virtualmin version 3.88.gpl GPL

i can login as root by ssh and can login in virtualmin as master admin with two account: root and myAccount.
root is also a webmin user, myAccount not.
myAccount is not admin for any virtual server, is the user I choosed as admin during installation.

Let’s say the password are “myPassword1234” and “myPassword5678” both them can log in virtualmin using only “myPassword”.
More, I was not able to change the myAccount password using webmin>System>Change Passwords or webmin>System>Users and Groups menus

Any suggestion?