Bantha

oh dear, sorry. 

I posted this both here and on DAZ 3D. 
The problem appears to have been temporary (I hope)  stupidity on my part, and my 'error' was pointed out to me (patiently, it has to be said) on the DAZ 3D forum.  I think it works OK now - have not had much of a chance to try it out throughly - but a quick check suggests that I got it wrong (after having used the feature so many times before).  It must have been 'one of those days'.

Many thanks for your response, and sorry for not updating this thread.

Regards
Peter