version 2.7.1 - 2.9.2
when MySQL is not properly configured and fails to insert a comment (e.g. in case of unsupported character in message), WordPress behaves inproperly; this error is not checked within the file /wp-comments-post.php and the user is redirected to an invalid page (.../wp-comments-post.php#comment-) without any message.
There should be a check, in /wp-comments-post.php:83
$comment_id = wp_new_comment( $commentdata );
/*check*/if (!$comment_id) wp_die( __('Error: unable to insert the comment, because ...') );