Hello people,
Many thanks for your replies, and apologies for my absence - posting to the forum a couple of days before going away was, in retrospect, not wise.
Anyway, I have upgraded to version 1.6.1 and the problem I had has resolved itself. I'm still not sure what was going wrong, but at least it's solved! I will let you know if I am able to reproduce it in the future ...
Thanks again for the assistance,
Geoff