Martyn,
Do you mind if I compare my CO Tones for Telstra.
Yep this is the same as what I use and don't have issues.
Andy, the only difference on that form is the delay time for what I would normally set is 7, instead of 10.
On the Circuit descriptor form try changing:
Calling party disconnect to yes.
Release Supervision Expected to yes
Flash Timer 200 (instead of 300)
Call Clearing Signal - Reversal
The above is what just gets imported every time that an analogue trunk is created (just have a CSV that gets imported, and then I don't miss anything), and there isn't generally any issues with these settings. I can't think of a time where I have had to change them, so they should be good. It might not solve the problem as there just isn't a solution, but it should at least help to reduce the amount of lock ups.
Unfortunately trying to compare settings to a UK (or any other country) system could end up leading you up the garden path, as generally Telstra have done it their way, which is often not the same way that every one else does things.