[Serusers] UAS binding

Hi, I have a problem with registering with a UAS when using SER as a stateful proxy. The UAS stores the UAC IP address in it's binding list. This IP address was obtained by the Contact header field. Now if the UAS receive a call and needs to contact my UAC, an INVITE is sent directly to the UAC IP address instead of sending it to the proxy for relaying. What is the normal behavior of a UAS when receiving a REGISTER that is coming from a proxy server ? Sould it save the proxy IP address in it's bindings table ? Another question: Is it acceptable per RFC for a UAS to rewrite the SIP VIA headers and concatenate them on a single, separated by commas ? Don't ask me the reason for this, but I have noticed a UAS doing just that and I need to know if this is just wrong or acceptable. Thanks, Jack