I just discovered a strange FB-box on my german-language-forum. At my english-language forum, this issue does not show up. At the registered members page of my XF-forum, it shows the Facebook-Login-box within the sidebar underneath of "Newest Members", although I am not logged-in into Facebook. I also refreshed the page, but this box still stays. Runnig XF 1.0.0 without any customizations.