Kamailio keeps increasing contacts:

#!KAMAILIO

## The following example will result in each subsequent transaction having it's rURI ADDED to the 
## contact header, causing it to grow.  For example, this would be the contact header of the third
## reply to this message:

## Contact: <sip:+16127359309@127.0.0.1:5050>, <sip:+16127359309@127.0.0.1:5050>, <sip:+16127359309@127.0.0.1:5050>

## Tested against Kamilio version:
## version: kamailio 5.5.2 (x86_64/linux)
## flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, 
## SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, 
## USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLOCKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED
## ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB
## poll method support: poll, epoll_lt, epoll_et, sigio_rt, select.
## id: unknown
## compiled on 23:35:51 Nov  2 2021 with gcc 10.3.1

loadmodule "corex"
loadmodule "tm"
loadmodule "sl"
loadmodule "xlog"
loadmodule "pv"
loadmodule "ctl"
loadmodule "textops"
loadmodule "tmx"
loadmodule "siputils"
loadmodule "http_async_client"
loadmodule "jansson"
loadmodule "uuid"
loadmodule "cfgutils"

!!defenv CNAM_URL


#modparam("http_async_client", "curl_verbose", 1)

force_rport = yes

# -------------------------  request routing logic -------------------
route {
    xlogl( "L_INFO", "[rt route][$ci] Request Received [$rm] [$ru]\n" );

    if ( is_method("INVITE") ) {
        t_newtran();
        http_async_query( CNAM_URL , "HTTP_REPLY" );
        exit;
    }

    ## Just to handle ACK for this simple example:
    t_check_trans();

}

route[HTTP_REPLY] {
    append_branch();
    ## Possible solution:  Remove the append_branch() above, and comment out below:
    # $ru = $ru;
    send_reply( "380", "CNAM Response" );
    drop;
}