surprised to see different posts when logged in

Today I've been surprised to see different posts when logged in - specifically, in the corporate video forum, a whole thread disappears if I view logged in today compared to not logged in. If I disable third party cookies on your site (using webdeveloper in FF) the issue goes away - all the posts appear to become viewable again.

I have the same view options (View:New Today and View posts by Thread) selected, so it seems to be a third party cookie affecting post visibility ... strange.

Thanks