Windows Mobile 6 tapi and OpenNetCF telephone

Question

I have a Ciperlab scanner running Windows Mobile 6 and compact framework 3.5. I have developed a phone interface from the app using OpenNetCF Telephony. This works well but at times the "hangup" takes up to 80 seconds before the "disconnected" event is driven". The OpenNetCF "hangup" method is a simple wrapper for the native tapi "lineDrop" method. Calling "lineDrop" without using the OpenNetCF wrapper gives the same problem. To try to break out of the 80 second delay I have a timer. In the timer_tick event I have tried to dispose of and re-initialise OpenNetCF but this then hangs the entire program and I have to reboot. Any suggestions on what is causing this 80 second delay and how to avoid it / break out of it would be welcomed