BobC &
davidfor - I had a similar issue yesterday, I installed jackie-w's revised Count Pages (manually), restarted calibre via ctrl/r --- jackie's change wasn't in the config screen - WTF!
I checked to see if the plugin code in config/resources had jackie's changes - it did. So I restarted calibre in debug - whaddya know - jackie's new option was in the config panel
To be certain I installed jackie's PI in V2.22 portable, restarted, jackie's new config option was there. I was prepared to admit I was mistaken on first install
But after reading your post I'm not so sure. Something similar happened recently, I changed something that needed restart, a Tweak I think, and I had to do 2 restarts to make it 'stick' - again I blamed myself.
Makes me wonder if Windows is saying - 'ah, I already have an intact image of that loaded, so I'll just reuse it' - surely not
BR