I built K master and tried to use 5.2 config. That resulted in error: Apr 30 15:47:10 salmon /usr/bin/sip-proxy[1659]: ERROR: siptrace [siptrace.c:908]: w_sip_trace3(): no duplicate_uri modparam nor duplicate uri sip_trace() argument provided! I think it has been practice that backwards compatibility is provided by the next version.