Apparently one of the latest version updates of Wordpress is now issuing a true 404 header in response to a 404 condition. Previously, WordPress would simply forward the 404 to the custom 404.php and you could handle it without triggering a 404 on the search engine crawler. For example, you could load your Sitemap with a custom message for the user.
"We could not find the page you were searching for, however, you may find it below..." as an example.
With previous versions of WordPress, you actually had to manually send a 404 header if you wanted to do so.
Can anyone suggest a workaround to prevent the 404 headers?