asterisk users - Feb 2019 - Gigaset C610 IP error with PJSIP

Hi,

We upgraded an Asterisk 11 server to 16.1.1, going from chan_sip to 
pjsip, on a site using Gigaset phones. They are registring well despite 
the fact that we get a lot of errors like

[Feb 22 18:30:07] ERROR[1556]: pjproject: <?>:  sip_transport. Error 
processing 367 bytes packet from UDP 192.168.1.108:5060 : PJSIP syntax 
error exception when parsing 'To' header on line 4 col 51:
SIP/2.0 200 OK
Via: SIP/2.0/UDP 
192.168.1.250:5060;rport=5060;branch=z9hG4bKPjf89448cc-aeed-47be-b9a3-4e9b79f064bd
From: 
<sip:xxxxxxxxxxxxx at
192.168.1.250>;tag=9a7c1775-fe8d-4c67-a8a4-c44e5d473742
To: 
<sip:xxxxxxxxxxxxx at
192.168.1.108>;tag=8`6b0664,gd9e,5b76,`9`5,b55d4e562653
Call-ID: fd359d3b-1102-4cd5-929a-46a04a95389d
CSeq: 28722 NOTIFY
Content-Length: 0

It seems that the comma in the <To: > tag is the origin of this behavior.

Is this an Asterisk problem or a Gigaset one ?

Daniel