W60B DECT can't dial 911, using wrong port

[c.holloway]

I'm having an issue with ONLY the w60b DECT phones on a 3CX installation. The issue is that when calling 911, and only when calling 911, the phone is not using the correct SIP port. Instead of using port 3560 for the call, it goes back to the default of 5060 to make the call and thus fails. When calling any other number, it uses the correct port and the call goes through.

I have tried using the firmwares 77.83.0.20, 77.81.30, and 77.81.0.10 and it happens on all of them. I have attached pictures of the pertinent INVITE as captured by the pcap trace on the phone itself. The first attachment is the failed call to 911 and the second is the successful call to another number that uses the correct port.

This is a HUGE issue for us (and anyone really) that I need help with, any advise would be very welcome