I think this is a bug because the Yealink IP Phone SIP-T27G does not refresh the most recently received NOTIFY messages.
Following capture hint monitoring:
(05-17-2014 11:22 AM)Yealink Support Wrote: NOTIFY sip:5991@phoneipaddr:5060 SIP/2.0
v: SIP/2.0/UDP asteriskserveripaddr:5060;branch=z9hG4bK3ceecd02
Max-Forwards: 70
f: <sip:202@asteriskserveripaddr>;tag=as75cd87a9
t: "User Name 2" <sip:5991@asteriskserveripaddr:5060>;tag=190612704
m: <sip:202@asteriskserveripaddr:5060>
i: 0_472292147@phoneipaddr
CSeq: 103 NOTIFY
User-Agent: Asterisk PBX - OpenS Tecnologia
Subscription-State: active
o: dialog
c: application/dialog-info+xml
l: 558
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="1" state="full" entity="sip:202@asteriskserveripaddr">
<dialog id="202" call-id="pickup-0_472292147@phoneipaddr" local-tag="190612704" remote-tag="as75cd87a9" direction="recipient">
<remote>
<identity display="202">sip:202@asteriskserveripaddr</identity>
<target uri="sip:202@asteriskserveripaddr"/>
</remote>
<local>
<identity display="202">sip:202@asteriskserveripaddr</identity>
<target uri="sip:202@asteriskserveripaddr"/>
</local>
<state>early</state>
</dialog>
</dialog-info>
SIP/2.0 200 OK
Via: SIP/2.0/UDP asteriskserveripaddr:5060;branch=z9hG4bK3ceecd02
From: <sip:202@asteriskserveripaddr>;tag=as75cd87a9
To: "User Name 2" <sip:5991@asteriskserveripaddr:5060>;tag=190612704
Call-ID: 0_472292147@phoneipaddr
CSeq: 103 NOTIFY
Contact: <sip:5991@phoneipaddr:5060>
User-Agent: Yealink SIP-T27G 69.84.0.10
Content-Length: 0
NOTIFY sip:5991@phoneipaddr:5060 SIP/2.0
v: SIP/2.0/UDP asteriskserveripaddr:5060;branch=z9hG4bK7cd1503c
Max-Forwards: 70
f: <sip:202@asteriskserveripaddr>;tag=as75cd87a9
t: "User Name 2" <sip:5991@asteriskserveripaddr:5060>;tag=190612704
m: <sip:202@asteriskserveripaddr:5060>
i: 0_472292147@phoneipaddr
CSeq: 104 NOTIFY
User-Agent: Asterisk PBX - OpenS Tecnologia
Subscription-State: active
o: dialog
c: application/dialog-info+xml
l: 572
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="2" state="full" entity="sip:202@asteriskserveripaddr">
<dialog id="202" call-id="pickup-0_472292147@phoneipaddr" local-tag="190612704" remote-tag="as75cd87a9" direction="recipient">
<remote>
<identity display="User Name Extern">sip:22225555@asteriskserveripaddr</identity>
<target uri="sip:22225555@asteriskserveripaddr"/>
</remote>
<local>
<identity display="User Name 1">sip:5988@asteriskserveripaddr</identity>
<target uri="sip:5988@asteriskserveripaddr"/>
</local>
<state>early</state>
</dialog>
</dialog-info>
SIP/2.0 200 OK
Via: SIP/2.0/UDP asteriskserveripaddr:5060;branch=z9hG4bK7cd1503c
From: <sip:202@asteriskserveripaddr>;tag=as75cd87a9
To: "User Name 2" <sip:5991@asteriskserveripaddr:5060>;tag=190612704
Call-ID: 0_472292147@phoneipaddr
CSeq: 104 NOTIFY
Contact: <sip:5991@phoneipaddr:5060>
User-Agent: Yealink SIP-T27G 69.84.0.10
Content-Length: 0
NOTIFY sip:5991@phoneipaddr:5060 SIP/2.0
v: SIP/2.0/UDP asteriskserveripaddr:5060;branch=z9hG4bK4ece7870
Max-Forwards: 70
f: <sip:202@asteriskserveripaddr>;tag=as75cd87a9
t: "User Name 2" <sip:5991@asteriskserveripaddr:5060>;tag=190612704
m: <sip:202@asteriskserveripaddr:5060>
i: 0_472292147@phoneipaddr
CSeq: 105 NOTIFY
User-Agent: Asterisk PBX - OpenS Tecnologia
Subscription-State: active
o: dialog
c: application/dialog-info+xml
l: 210
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="3" state="full" entity="sip:202@asteriskserveripaddr">
<dialog id="202">
<state>terminated</state>
</dialog>
</dialog-info>
SIP/2.0 200 OK
Via: SIP/2.0/UDP asteriskserveripaddr:5060;branch=z9hG4bK4ece7870
From: <sip:202@asteriskserveripaddr>;tag=as75cd87a9
To: "User Name 2" <sip:5991@asteriskserveripaddr:5060>;tag=190612704
Call-ID: 0_472292147@phoneipaddr
CSeq: 105 NOTIFY
Contact: <sip:5991@phoneipaddr:5060>
User-Agent: Yealink SIP-T27G 69.84.0.10
Content-Length: 0
Yealink's software engineering should correct this behavior so that the device displays the correct group user information, as soon as possible.
