SIP NOTIFY missing Subscription-State?

Hi, I’m wondering why Asterisk is not putting the header
Subscription-State when sending notify…

My users are not registering on asterisk, so i just set them up as peers, and it’s fine, asterisk is sending the notify after a subscribe request, but unfortunatly it seems the switch (Tekelec t7000) where my users are registering is expecting the header:
Subscription-State: active

And asterisk is not sending it… is that normal behavior?
If it is, i guess i’ll have to modify the source of chan_sip.c
to send the header i need

Here’s a SIP message sent by asterisk:
[i]NOTIFY sip:xxxxxx8528@xx.xx.xx.41 SIP/2.0
Via: SIP/2.0/UDP xx.xx.xx.42:5060;branch=z9hG4bK11587b90;rport
From: “asterisk” sip:xxxxxx8528@xx.xx.xx.42;tag=as3d15aab6
To: sip:xxxxxx8528@xx.xx.xx.41
Contact: sip:xxxxxx8528@xx.xx.xx.42
Call-ID: 61dd076a51d5e6cd2adbeae526f4bf1e@xx.xx.xx.42
CSeq: 102 NOTIFY
User-Agent: Voicemail
Max-Forwards: 70
Event: message-summary
Content-Type: application/simple-message-summary
Content-Length: 94

Messages-Waiting: yes
Message-Account: sip:asterisk@xx.xx.xx.42
Voice-Message: 9/1 (0/0)[/i]

And then unfortunatly the switch responds with a:
SIP/2.0 400 Bad Request
Via: SIP/2.0/UDP xx.xx.xx.42:5060;branch=z9hG4bK11587b90;rport
From: “asterisk” sip:xxxxxx8528@xx.xx.xx.42;tag=as3d15aab6
To: sip:xxxxxx8528@xx.xx.xx.41;tag=THkf00fl5dhR21Hatxx.xx.xx.41
Call-ID: 61dd076a51d5e6cd2adbeae526f4bf1e@xx.xx.xx.42
CSeq: 102 NOTIFY
Content-Length: 0