[OpenSER-Users] CANCEL with Route headers

Hi all, I've a Cisco PGW interconnecting with an OpenSER server. The INVITE is sent to OpenSER, which does some record-routing via some different hops and then sends back the 180 from the called party. If the calling party now cancels the call, the PGW tries to loose-route the CANCEL by adding the Route header to the CANCEL and altering the R-URI, which is rejected by my OpenSER since I don't allow initial loose-routing. So the question is: is it valid for a CANCEL to carry a Route header which wasn't available in the INVITE? §9.1 of RFC3261 says it MUST contain the Route header if it was present in the request being cancelled. What about the other way around? I heavily suspect it's violating the RFC since CANCEL should be more or less a 1:1 copy of the INVITE, but can anyone confirm this? If it violates the RFC, anyone with some Cisco knowledge who knows how to disable this behavior, or is it a known bug? Cheers, Andreas