Hi,
You didn't mention the phones that you are using. We had a similar
problem (or at lease similar symptoms) when a call from a SPA-841 is
"rejected" by a Polycom-500. In this situation, the SPA-841 still kept
ringing.
Below is the final in a series of emails I received from Sipura:
<snip>
You have uncovered a bug in our firmware.
In fact all 6xx responses will be ignored by the phone.
A temporary fix is available at:
http://www.sipura.com/download/temp/phone/spa841-03-01-03-a-0427s-603.zip
Thanks for reporting back the problem.
- Sipura Support
</snip>
Regards,
Norman Brandinger
norm at goes dot com