We’ve made some changes to domain_mapping.php to include support for the redirect_to querystring option as all query string variables are stripped out when a javascript redirection occurs.

This can be replicated on a mapped domain which requires logins before commenting and has been confirmed on WPMU 2.9.2 – I haven’t tried 3.0 yet.

It’s about 20 lines but if you would like to consider it, please contact me via email – I’d be mostly appreciated. Thanks.