There is a SEO rule, where 1 page content must have exactly 1 (and not more) url to it. If page content changes you:
- either must send proper caching headers (which In-Portal doesn't do at all)
- or change page url
But if we show user-specific content (content that is one for logged-in users and other for non logged-in users) on a page, then, because we have same url to that page, browser can agressively cache it resulting after logout user being presented with logged-in only page version.
This wasn't a problem before, but now once Google Chrome v21 (with MacBook Pro Retina support) is out it actually used it. I saw this on Vista (not Windows 7):
- visit website (you're not logged in)
- see "please login" sidebox on the left (while on home page)
- login
- browse through website
- press logout link
- see logged-in side box on the left instead of "please login" side box
Despite long story problem is quite easy to fix - just add "?logout=1 or ?logged_out=1" parameter to page url where user is redirected after logout.