In the english language file, the base message to appear in forums in the case of not logged-in guests,
"Only registered users are allowed to post here. Please, enter your username/password details upon posting a message, or register first."

The last words are a direct link to the register form, allowing a new guest to register even when the main register option on the front page has been disabled by the setting $enableNewRegistrations=FALSE

In my case, I simply removed that part of the text in the language file to prevent unwanted user registration. You should at minimum make a comment at the part of the manual handling $enableNewRegistrations=FALSE, or add code to check the setting and remove the link if new registrations are blocked.

Thanks a lot for your suggestion / notice.

Even if such a direct link is present, it will lead to the starting forums page in the case of $enableNewRegistrations=FALSE, so registration won't be possible anyway.

However we'll take your suggestions into the consideration upon releasing the newer version of miniBB, which should come in September.

Unfortunately that is not the case. The link is the same override you gave in your manual to enable the admin to register someone, and it goes not to the main page but to the "confirm acceptance of the rules"-page of the registration process.

The code (copied directly from the eng.php file) is

Yes - but it should happen only if you're logged-in as the Admin, or does it happen also to all guests?