My Panasonic cordless phone does not disconnect when the far connection hangs up

 I have VIOP phone service from Comcast and am using a Netgear CM1150V modem. Mu phone is a Panasonic cordless phone.

The problem is after a connection is established and then the far end hangs up (disconnects) my Panasonic cordless does not automatically disconnect from the line unless I manually hang it up.

This results in the my number showing Busy to Comcast preventing any incoming calls. This has happened often with the bussy state,  onetime lasting oner 11 hours before someone realized this and hung up the phone.

This condition is most likely caused by faulty operation between phone and the modem. I have contacted Comcast who tells me since I own the modem that will not help. Netgear has been no help since since I can not find anyone there who knows what the handshake betreen and phone is. Panasonic is equally unhelpful. They tell me should work but ay unable to explian what the handshake should be.

I have looked at the log in the modem and see all the expected messagef to/from Comcast's end.

Has and else seen this?