errorpage: wrong images URL's and misbehaving back button

If you attempt to log in using not-allowed characters
in the loginname an error page appears on which:

1. The images of logo's are not found because their URL
contain a "/" extra, e.g.
themes//img/logo.png instead of themes/img/logo.png and
themes//img/button.png instead of themes/img/button.png

2. The Back button, that links to /nocc/action.php does
not work, you remain on the same error page (session
stuck?) after you click it.

Configuration:
NOCC 1.3-dev (CVS build 2006-08-24)
PHP 5.1.2 as module under Apache 2.2.0
Windows XP Pro SP2
in php.conf: $conf->allowed_char='^[a-zA-Z0-9_]+';