asterisk users - Jul 2006 - Echo cancellation doesn't work after inbound calls are transferred to another extension

When the call is then transferred by an operator to an internal extension
the receiver of the call finds that they get a lot of echo, for the entire
duration of the call. It seems that echo training isn't working, or the
canceller is disabled somehow after the call is transferred by the operator.
The remote/external end of the call has no problems with echo (just our
internal side).

When the call comes in initially to the operators they complain of a
momentary echo which lasts a few seconds but goes away (I presume this is
just echo training at work) - I would love to get rid of this echo but I can
live with it for now. 

The calls are being bridged from a TDM400P FXO connected to Telco to SIP
SNOM320 (operator) and then transferred to another SNOM320 or Grandstream
BT101.

Does anybody know why transferred calls get echo and how I can fix it?

Thanks

Jared


Some info:
---------
I am running asterisk asterisk-1.2.7.1 with bristff patched in
(bristuff-0.3.0-PRE-1p). Reason I am using bri is solely for the Devstate()
app to light my SNOM LEDs.

I am using both SNOM320 and Granstream BT-101 handsets.

I have configured 3 TDM400P cards also to handle inbound lines from our
telco (Telstra) in Australia.