I certainly hope this is a bug, not a feature, but the Navbar Replacements only work when I am logged in to the forum. as soon as I log out, the URLs loose the proper forum prefix and stop working.
actually, I have identified the problem. both of us are right. navbar replacements only will always if the board is turned ON. however, when you set the 'Forum Active' setting to No and log out, navbar replacements stop working.