- do not apply NAT contact fix of UAS when not usrloc forwarded

etc/sip-router-oob.cfg

@@ -359,7 +359,9 @@ flags
   FLAG_NAT_REG        : 14, # the UAC behind NAT, stored in location record
   FLAG_INIT_DLG       : 15, # init INVITE dialog
   FLAG_REVERSE_DIR    : 16, # set if request goes callee -> caller direction, requires rr.append_fromtag=1
-  FLAG_ACC_MISSED     : 17; # the missed call will be recorded by ACC
+  FLAG_ACC_MISSED     : 17, # the missed call will be recorded by ACC
+  FLAG_USRLOC_FWD     : 18, # usrloc based forward
+  FLAG_NEXT_ROUTE     : 19; # there is a route remaining
 
 avpflags
   dialog_cookie;            # attribute will be stored in Route headers
@@ -853,6 +855,19 @@ route[UAS_NAT_DETECTION]
 		break;
 	}
 
+	# prevent contact overwriting when a proxy between ser and UAS.
+	# We get it from record-route but it's rather difficult or
+	# do it only for UAS which is registered in usrloc database and has no
+	# proxy on path.
+	# Note: destination forced by $fwd_always_target is not NAT detected and contact left untouched!
+	if (isflagset(FLAG_INIT_DLG) && !isflagset(FLAG_USRLOC_FWD)) {
+		break;
+	}
+	# for in-dialog requests we get it easily because it provides loose_route()
+	if (!isflagset(FLAG_INIT_DLG) && isflagset(FLAG_NEXT_ROUTE)) {
+		break;
+	}
+
 	# Prevent that we over-write the Contact with the IP of our proxy when
 	# the reply loops through ourself.
 	if (src_ip == myself) {
@@ -931,6 +946,9 @@ route[PROCESS_ROUTES]
 		if (!defined $dialog_id) {
 			$dialog_id = $t.dialog_id; # there is only 1 dialog_id
 		}
+		if (@rr.next_route != "") {
+			setflag("FLAG_NEXT_ROUTE");
+		}
 		xlog("L_DEBUG", "\n%mb\n\ndialogid -/from/to=%$dialog_id/%$f.dialog_id/%$t.dialog_id");
 		if (method == "INVITE" || method == "UPDATE" || method == "ACK" || method == "BYE") {
 			if (!defined $dialog_id) {