Odd behaviour with WebSphere Portal

when HTTP_REQUEST {
    Disable the stream filter for all requests
   STREAM::disable
}
when HTTP_RESPONSE {

    Check if response type is text
   if {[HTTP::header value Content-Type] contains "text"}{

       Replace http://www.server.com:80/wrc/fff with https://www.server.com/wrc/fff 
      STREAM::expression "@http://www.server.com:80/wrc/fff@https://www.server.com/wrc/fff@"

       Enable the stream filter for this response only
      STREAM::enable
   }
}