Sip trunk port cant be same as bind address

Sip trunks will no longer connect by either pjsip or chansip if they have the same bind port as the sip trunk.

For example sipgate.co.uk trunks require port 5060, if I try to set up a trunk using pjsip (on bind port 5060) the provider does not respond to registration requests. If I change the bind port for pjsip to anything other than 5060 it all works fine.  

The same happens if I use legacy chansip (the bind port cant be the same as the sip trunk port). The wireshark trace does nor see any response from the registration request.

This was never a problem in the past (version 13.0.197.28) in fact many tutorials say its best to use 5060 at both ends.

Because sipgate.co.uk required port 5060 for sip trunks moving to the new version of FreePBX would be extremely problematic. Please can you help ?