Assuming ds_probing_mode = 0 (Only send "ping" requests when destination is in probing state)
AP (Active-Probing) [*] Used by ds_select_* in gateway selection [*] Ping probes sent to destination [*] When reply to ping probe is recieved, state for gateway chages to AX (Active)
Testing with dev branch, then the above is true. Dev branch will use destination if it is in active-probing state. Kamailio version to test this is:
# sbin/kamailio -V version: kamailio 3.3.0-dev0 (i386/linux) 25bedc flags: STATS: Off, USE_IPV6, USE_TCP, USE_TLS, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MEM, SHM_MMAP, PKG_MALLOC, DBG_QM_MALLOC, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES ADAPTIVE_WAIT_LOOPS=1024, MAX_RECV_BUFFER_SIZE 262144, MAX_LISTEN 16, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 4MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: 25bedc compiled on 09:18:41 Oct 21 2011 with gcc 4.1.2