Geoff,
An even more annoying problem was that on Window, if you restarted PI quickly (a few seconds) after shutting it down, it was creating a "second" instance (although the first one was not visible anymore). This behavior, combined with the separate settings for the second instance, was very confusing.
Some people think that it was due to Virus or malware. But in fact it happened quite systematically if you had very large workspace/ many files / may be large swap file?. Even on system with light or no antivirus (and unlikely to be infected). I think that the main thread was still present and detected, maybe while windows was releasing memory (possibly clearing temporary space or doing whatever it feels was needed). I have no definitive explanation, but it was simpler to ask Juan to change PI than Bill to change W7
As for the settings, the sharing may not be easy due to the way PI write them (who win in case of multiple write?). You do not want to implement a database with locking, consistency checks, ...Maybe an option to open the settings read-only so a new instance can use the main settings? But I think that Juan has a lot of more important things to do and the current situation is adequate for me.
-- bitli