[SR-Users] loose_route() with pre-loaded Route in ACK

Hi, I ran into an interesting scenario when experimenting with kamailio 3.1 as a stateless proxy (no tm module used): There is an initial INVITE without to-tag and with pre-loaded Route header pointing to the external address of the lb. When I call loose_route for that, it returns false and the Route header is removed. That's what I expected, and it's documented in http://www.kamailio.org/docs/modules/3.1.x/modules_k/rr.html#loose-route-id. However if a 407 is relayed back from the registrar via the lb to the UA, it sends an ACK, again with pre-loaded Route header like in the initial INVITE, this time with to-tag. In that case, loose_route() returns true, but the $du is $null and the R-URI is still the same. So the Route is consumed, but the URI is not used. Since it's a stateless proxy, this hop-by-hop ACK needs to be routed the same way as the initial INVITE, so what I'm doing is something like that: if(loose_route()) { if($du == $null && $ru == $ou) { # skip loose-routing for such a request } } Is this how it's supposed to work? And is there some documentation of how loose_route() detects whether Route points to itself or not? I'm not using auto_aliases, nor do I set any aliases manually. Does it determine internally whether the Route points to its local ip and port? If not, how come the $du is not set although loose_route returns true? Andreas