It is not an error. The option does not allow users to see the question page, but lets everyone see the list of questions.
You can try to view the question without logging in and you'll see the message for the user to login or register.
To do what you want, unfortunately, there is no option in the core right now.
But, it is possible:
- There is the "Closed site" plugin.
This plugin is paid for and is a bit old. Unfortunately the developer is no longer active in the development of Q2A. This plugin may not be compatible with newer versions. But you can contact the developer and ask if the plugin is compatible and if it is being sold yet.
- You can either modify the core or create a plugin of your own:
In these questions there are tips and codes to do what you need and similar modifications.
Make these modifications on a test site first. These codes have not been tested and may not be compatible with the current version of Q2A or with some plugin.