(Help) chan_unistim Terminal ID question

I’m running Asterisk 1.6.0-beta8 on CentOS and am trying out the unistim functionality with 2 old i2004 phones. Both phones appear to be working properly and I can call to/from/between them, however I noticed in a Wireshark packet capture that the unistim Terminal ID is the same for both phones. I expected that it would be different for each phone. Can anyone confirm that it should be always the same or do I have a configuration issue?

Wireshark description (for some packets coming from either phone’s IP):
UNISTIM Payload: Aggregate Unistim with Terminal ID (0x02)
Terminal ID: 0.0.0.19 (0.0.0.19)

Both phones and Asterisk are all on the same subnet.

Unistim.conf:
[general]
port=5000

[phone1]
device=000aeXXXXXXX
line => 102
rtp_method=1

[phone2]
device=0060XXXXXXX
line => 103
rtp_method=1

extensions.conf:

[ext-unistim]
exten => 222,1,Dial(USTM/102@phone1)
exten => 111,1,Dial(USTM/103@phone2)