Ahaha... Hmm ok, that was one if my runs! you just quoted from the the file I posted. I did a few more runs, starting from that state, with the set to nothing switch true and got similar results for a while and then it went back to the behaviour I described earlier where the working set returns to close to the initial value. Looks like I've got some more investigating to do...

Thanks for that code and the link, I'll take a look later...
Still much to learn!