301 iRule redirection generating an extra 301 status code?!?

Can you add logging information to the irule and check in ltm logs (/var/log/ltm in cli or System >> Logs >> Local Traffic in GUI) :

when HTTP_REQUEST { 
    if { [string tolower [HTTP::host]] eq "sitename.com" } { 
        log local0. "vs_name=[virtual], 301 redirect to https://www.sitename.com[HTTP::uri]"
        HTTP::respond 301 Location "https://www.sitename.com[HTTP::uri]" Test TestRedirect Connection Close
    }
}