on a new WP blog, custom template, some hacks, single posts are displayed, but a header 404 is sent.
After some search, the header is sent by $wp->handle_404(). Somehow it manage to match all conditions (including count($wp_query->posts) == 0) and send a 404 error.. .while displaying the post.
Not a problem for my visitors but bad for Google.
Has anyone seen this problem before ?