LinkItem with external URL not redirected to login when called by direct link

Links to other Albums created with the LinkItems module redirect to the login page as required by permissions. These permissions are also adhered to when the LinkItem is accessed externally by a direct link (e.g. http://testserver/gallery/v/linkitem7731.html).

However when the LinkItem contains an external URL, the direct access will return the output directly even when from this LinkItem all permissions have been removed.
It appears to me that not the permissions of the LinkItems themselves are checked, but instead the permissions of the items referred to.
What I need is a LinkItem with an URL in Gallery to a trusted website, but this URL only to be available, also with an direct link, when logged in on Gallery2
Any suggestions where and how I can make a tweak so that in all cases access by a direct link to a LinkItem is controlled by the permissions of the LinkItem itself?