Hi,
The web host I use has standard expires headers for requests, but this isn't overridden by the admin.php file. So at home where I use the squid caching proxy I log into the admin panel on one computer, then browse to it from another machine connected to the proxy and I can get to the admin panel. Also any changes I make within the admin settings go back to what they were unless I do a hard refresh.
My solution was to edit the admin.php file to add:
header('Cache-Control: no-cache');
to the top.