Occasionally, the site will think I am still logged in even after I have clearly logged off. (And trust me, I thought I was just going nuts.) I could log off then visit again sometime later, and it shows I had been online.
Also, just now I was not logged in, and the box with 'New reply in a post you're watching' popped up. My username was not on the list and the login button read 'Login', ensuring me through this madness that I was in fact, not logged in.
I usually am on the site with Safari on my phone, maybe that's the problem? This hasn't started happening until recently.