My understanding is the auto-login does not bypass your authentication password, it simply bypasses the Ubuntu login screen where you enter the user password and skips right to your desktop. You still need to authenticate with the superuser password once you reach the desktop.
It is important to note, the authenticating password is different from the user password, so while the Automatic Login is checked, that just means you do not have to enter your user password. If you want more info on the authenticator keyring, pls check this thread.