Comment 26 for bug 1257186

As Thomas (reusch) suggest in #14 :
run "pam-auth-update" and remove "SMB password synchronization".

This isn't a security issue, simply you must remember that your samba password may not match your system password.
In an enterprise enviroment, if ubuntu is used as samba server, i bet it use kerberos tickets to verify the users identity throught domain controller or alternative ldap infrastructure.