Buggy no-password user logout

I have 3 user: The administrator one with password, and the other 2 are standard without password (I eliminated the password by `sudo passwd -d username`).
If I'm logged in a no-password user and I logout, the screen goes black (It goes back to the login screen) and after that it logs in the same account. That's because if you select a user (Whithout password) in the login screen, it logs in inmediatly.
When you log out, that account is represented as the selected one in the login screen, so if you log out with a no-password user, it selects that one, and it logins in that one inmediatly.