I am finding various weirdities if I check the box to keep me logged in, go away for a period of time, and then come back to see if there are any new posts.
Sometimes I am still logged in as before, and all is cool.
Sometimes I am not logged in, and I have to re-log back in, even though I've only been away an hour or so. However, the redirect page from the login is invalid, but if I go back to the forum link, everything is fine.
Sometimes I am still logged in, but all of the icons on the left side indicate there are new posts to read. Even if I go into the forums, and use the mark thread read, and go back to the top level, and hit refresh, all of the forums indicate unread posts.
I use Google chrome on an old Fedora 11 system, but it is a back level version (26.0.1410.63-192696). Note, I read pjrc.com from several systems (Fedora 11, Fedora 19, and RHEL 6.5).