Aahh - sorry, I wandered away from this thread as I had so many problems.

I HAD to start running threads (since 2-3 days ago) as the problems with double posts were out of control.

Everything has now been resolved with the take-up of threads.
I don't know what the answer was, never will now.

But I'm happy with threads.

(Flood check was enabled BTW)
... is it possible it was something to do with spider friendly urls, maybe?