On my server running IIS 6.0 after a comment was posted the user was not redirected back to the post page. I tracked the issue back to the wp_redirect function in pluggable-functions.php. The function checks if the server is IIS and if so uses an alternative version for redirection. The file contains a reference to a MS knowledge base article that discusses a bug in IIS 5 that necessitated this fix. However, it appears that this fix on IIS 5 was breaking my server on IIS 6. I rewrote the function to always use the default version and my system is working fine.
Hopefully this is fixed in v1.6 but I wanted to report it. Hope this is the correct place.