Well one thing that I think is established - it has NOTHING to do with 
cache whatsoever. The refresh button is there to refresh, and that means 
overriding the browser's cache. If the server itself has cached the page, 
so what, it'll just return the same default page back to the browser and 
back to the start you go anyway!
The answer seems to be this. If the frameset page ends is .asp then the 
refresh button causes the frameset page to refresh (resetting the frames 
back to the start). If the frameset page is .htm then the refresh button 
only refreshes the frames themselves, the frameset page is not refreshed, 
it doesn't seem to even get considered for refresh until the user types 
the URL in the browser again.

So maybe a way around this is to store current frame urls in a cookie and 
then read the cookie from the frameset page.

Thanks all
Matt