Have a look that this source code:

// Lowercase via is used by open proxies/referrer spammers
// Exceptions: Clearswift uses lowercase via (refuses to fix;
// may be blocked again in the future)
if (array_key_exists(’via’, $package['headers']) &&
!strstr($package['headers']['via'],’Clearswift Web Policy Engine’)) {
return “9c9e4979″;
}

Hm….

4.2 Message Headers

   HTTP header fields, which include general-header (section 4.5),
   request-header (section 5.3), response-header (section 6.2), and
   entity-header (section 7.1) fields, follow the same generic format as
   that given in Section 3.1 of RFC 822 [9]. Each header field consists
   of a name followed by a colon (”:”) and the field value. Field names
   are case-insensitive. 

Well, it seems that: Clearswift, Coral CDN, etc are getting blocked because of this…

If you use Bad Behavior let me know you experiences with it, and if this is affecting you, you might want to contact them.