I had the same problem, not fixed in 2.8 either.
I ended up in disabling the canonical redirects all at once (the bug is in wp-includes/canonical.php). To do that, as suggested here, I created a plugin called disable-canonical-redirects.php which contains the following code:
<?php
/*
Plugin Name: Disable Canonical URL Redirection
Description: Disables the "Canonical URL Redirect" features of WordPress 2.3 and above.
Version: 1.0
Author: Mark Jaquith
Author URI: https://markjaquith.com/
*/
remove_filter('template_redirect', 'redirect_canonical');
?>
Upload the file in wp-content/plugins and activate it from the Manage Plugins page as usual. No problem of weird redirects anymore :=)