Log out, doesn't actually log out

I'm having yet another issue.

When I log out of my site, I get sent to the correct redirect page (home), and the user appears to be logged out, however once the user clicks on a different page, it shows to still be logged in. Why??

If you need to see what I'm talking about.. I've setup a test account.

The site build is: volumeco.com/wp
Test user is: drum1234567890
Password: testy

It's a bit frustrating.. any suggestions?