Your comments

Yes, I noticed the thread on the other bug and thought they were likely to be related... meant to comment. Good work fixing it, anyway.

Yes... as I say, things always seem simpler from the outside, I do appreciate how it all gets much fiddlier when faced with the reality... :)

OK (although I don't really understand why all previews don't also need to have the appropriate sub-program compiled separately, or how the compilation would involve anything other than concatenating the relevant strings... clearly one of those things that seems simpler from the outside; if you say it's harder I'm sure it is).