Comment 9 for bug 835310

Andy, your logs showed you logged in as "administrator", returned to the greeter but failed to authenticate correctly as "administrator" then you tried the test account. What happened after entering the password for administrator?

There was as fix recently in bug 783598 where PAM could display some information without a prompt and lightdm wouldn't handle this. Is there anything special about the administrator account / does it do anything more complex than username/password in another display manager (e.g. GDM)?

This may also be related to bug 851612 where lightdm requests to switch back to the previous session but it doesn't work for some reason.