We have a domain resolving to our AEM environment and we are seeing this issue.
A call using the domain "http://staging.thissite.com/page" will not retrieve the content at /content/site/en/page.html however we do get the site custom error page.
If the content has been cached previously using "http://dispatcher.url.com/content/thissite/en/page.html" then it will be served correctly using the URL above.
So our virtual host redirects are working and do point to the cache location but will not make the dispatcher retrieve the content if not already cached.
Our dispatcher logs are set to debug(3) but we are not seeing any entries except for the single call and a 404.
The one difference between the two calls that I can see is that during the 404 we are getting [publishfarm/0] and during a successful return we are getting [publishfarm/-].
Son of a gun. Good call.