Thanks for the offer jimmy.
However, I've just had a "moment of clarity", and everything has suddenly clicked into place.
It was one of those *slap yourself on the forehead* moments when you suddenly realise that you've been doing the simplest thing wrong all this time.
So ... I'm glad to say that right now everything is working as it should!
I'm sure that I'll be back again once I have my next problem though!
Thanks.
--David