Yes, incoming DID is broken. Sometimes it will work. No rhyme or reason when or how. I am finding Kamailio to be a PiTA to troubleshoot. Even with debug enabled the logging is almost useless. No easy way to trace a call through the configuration script.
Really makes you appreciate Asterisk logging.
I'm using this for debugging http://kamailio.org/docs/modules/4.2.x/modules/debugger.html