Problems with Windows Messenger 5.0 SIP Capabilities

With 5.0, Windows Messenger no longer seems to listen on
port 5060 (SIP default port). Is this true?

When you sign into a SIP Communications server, Messenger
picks a port,

REGISTER sip:site.com SIP/2.0
Via: SIP/2.0/UDP 172.16.129.251:12150
Max-Forwards: 70
From:
;tag=9951adb9ce614b0f9fe695f4 7a2cdc02;
epid=276d64c3bd
To:
Call-ID:
CSeq: 2 REGISTER
Contact: sip:172.16.129.251:12150;methods="INVITE,
MESSAGE, INFO, SUBSCRIBE, OPTIONS, BYE, CANCEL, NOTIFY,
ACK, REFER"
User-Agent: RTC/1.2.4949 (Messenger 5.0.0468)
Expires: 0
Event: registration
Content-Length: 0

In this message, Messenger has requested port 12150 to
received SIP messages. The 200 OK is sent to the port but
Messenger doesn't seem to be listening there.

This is true for SUCBSCRIBE's as well.

Has anyone else experienced this?

Thanks.