Have you inserted the track by confirming the preview with Apply?
If the assistant is closed (e.g. by clicking somewhere outside the assistant) without actually inserting a track the preview disappears and no changes are made to your layout.
Hope this makes sense,
Thank you very much. I hadn't seen / noticed the 'apply' box - I was looking at the track, not anywhere near the place where the box appears....there's none so blind as those that cannot see...!! I can confirm that the smart insert is working very well - it is just the operator who is faulty!!
PS many thanks for the swift reply, much appreciated