Hi blackone!
Thank you for testing and for reporting this issue.
Unfortunately, I haven't been able to reproduce that behaviour yet. During my tests (and there have been many), I could log in by entering username and password on the screen presented by lightdm every time.
Could you please give us some more details on your system and especially on that issue itself, that is to say what happens in detail when using lightdm (including your input) and how you do log in alternatively exactly (you mentioned openbox). Do you use some special chars in your username and/or realname? Is there anything noteworthy to read when you move to a tty after that error has ocurred?