On Ubuntu 12.04, if pam_conv is enabled users are unable to log into webmin - it rejects them with "Login failed. Please try again."
Upon looking at the logs it shows that webmin is attempting to first log in to PAM with no password (Imediately when user submits username) and then when they submit the password, it attempts to log in with just the pssword nd no username,
perl: pam_unix(webmin:auth): authentication failure; logname= uid=0 euid=0 tty= ruser= rhost= user=suolirav
webmin: Non-existent login as unknown from 22.214.171.124