I have a scenario where calls that are transferred to a shared line doesn't trigger the "in use" light to show up on both phones that have the shared line. 

but when i make an outgoing call, let's say, using the shared line, the "in use" light lights up on both phones that have the shared line. 

Phone - polycom 650s.

Just a noob with SIP, kamailio and telecom, so not sure where to start debugging. 

Any suggestions would be appreciated. 

thanks in advance for your time.