Synopsis: mailformed header in the case of 503 code State-Changed-From-To: open-closed State-Changed-By: marc State-Changed-When: Sun May 24 17:43:23 PDT 1998 State-Changed-Why: Nothing to do with Apache. The sites in question have probably installed some software designed to limit the number of requests being served.
A default install of Apache won't do this, and there really isn't anything wrong with the results being returned.
