HTTP::header insert and header names

HTTP::header should insert it exactly as given. It does not prepend "HTTP_" on my system:

 
 when HTTP_RESPONSE { 
   HTTP::header insert headername headervalue 
 } 
 

gives

 
 HTTP/1.1 200 OK 
 Date: Tue, 02 Jun 2009 22:26:02 GMT 
 Accept-Ranges: bytes 
 Content-Length: 45 
 Connection: close 
 Content-Type: text/html 
 headername: headervalue 
 

and doing it for requests works similarly. Perhaps you should try logging the contents of the parameters you pass to HTTP::header.