When I do not save over a patch using the same name, Structure works perfectly. It's probably a better work flow to save incrementally with different names, anyway.
Thank you for the much needed information.
As one thing leads to another, I've started a new thread with a related question that has now arisen.
Maybe one of you can shine some light on the following:
http://duc.avid.com/showthread.php?t=290754
Thanks again