[SR-Users] To-Tag on Register Refresh method

Hello all, I'm using Kamailio as a registrar and i have an endpoint that sometimes sends a REGISTER method with a To-Tag when refreshing its regist. My code on this proxy shares many similarities with the default kamailio.cfg configuration file. On that occasion Kamailio answers with a 404 - Not Here since it treats it as a in-dialog request which fails the loose_route check. Why would a CPE send a REGISTER with a To-Tag? Why is a REGISTER with a To-Tag rejected by Kamailio when it could otherwise be a successful REGISTER? Is this behaviour noncompliant with the SIP protocol? I thought about making an exception in the code and having this register following the same path as a register without to-tag, but i don't know if that is unsafe and/or noncompliant with the protocol. Best Regards,