After the new update 3.2.0.beta4-dev (24532653e6 )
This option not working any longer.
Provides more details to users about why they can’t access a particular topic. Note: This is less secure because users will know if a URL links to a valid topic.
What happens? just a standard 404?
Earlier when it was enabled private groups, catagory, shows message that you need to join the group in order to see it and there was join button also, but now even when this option is enabled it only shows this page doesn’t exist or is private.