asterisk users - Jul 2006 - Hangup detection with Sangoma A200 in the UK?

I'm having real problems getting my Sangoma A200 card with FXO board in to
detect hangup at all.
Basically if the remote end hangs up the call, Asterisk does not seem
to detect a
hangup.

A month or so ago I was running a system with 2 x X101P cards in, this
detected hangup fine.
Since switching to a Sangoma A200 based system hangup is no longer detected.
I've tried tweaking busydetect, busycount etc but it seems to make no
difference.

I'm using a system based on Trixbox, which is Asterisk  1.2.9.1  with
Zaptel 1.2.6, wanpipe drivers are Beta4-2.3.4.

Is there any good way of debugging this that I have missed?

thanks
Mike
UK