Login not possible without 'www' in URL

[phs]

Hi all

I have a problem regarding the login to Roundcube 1.0 without 'www' in the URL.

Login without the @ part of email address as username works with the following URLs:
​http://mail.domain.tld
​http://www.domain.tld/mail

But it does not work with the following URL:
​http://domain.tld/mail

I've opened ticket http://trac.roundcube.net/ticket/1489858 and described the behaviour. I tried all possible values for "$config['username_domain']". %d and %t have the same behaviour as described above (2 URLs work, 1 URL does not). All others do not work at all when trying to login without the @ part.

Furthermore I attached the imap log and my config.inc.php.

Maybe somebody can help me to identify the problem.

Regards