What Steve mentioned makes a lot of sense to me. New users or guest users, by the way, are not being impacted by this bug. It seems to be only with some "old" users. It does happen to me.
Rus, let me share some more IT details to explain what happened when you refreshed the page and you were then logged-in in all tabs.
Web browsers manage the access to a given site as A session. You can open multiple tabs as Guest and they are all the same session, just different screens. When you log-in in one tab, a new session is open in that screen. All open tabs are like a picture of that you last did in that tab and will keep unchanged. If you refresh a given tab, the browser will notice there is one new session that you recently opened in one of the tabs. Hence all tabs will show the "new picture" under this username session.
Since the bug is affecting "old" users and you just logged-in then post disappeared.
Does this help to understand what had happened with your tabs?
Cheers!
Chris