Hi. It seems that what you're referring to there is actually a security feature. It will only show posts made in boards which you (the viewer) can access. If a board is password protected then the system will presume you do not have access to it until you have entered the password. Once the password has been entered (once per Internet session) it will know you have access to that board and as such will include posts made in that board.

I hope that's understandable. Bearing in mind it's gone 2.30am I could be talking gibberish