User can see empty folder instead of getting an Access Denied Page

Well I have never seen anything like this before, regarding permissions.

Any user can navigate directly (using the link) to a folder in a document library and it will be empty.

However when I select the folder > Document Permissions > Check Permissions > The User has None. The folder has unique permissions, and definitely the user is not listed there. I've tried this with different users and all of them can see the empty folder even though they don't have any permissions.

So where's the Access Denied page?

On the other hand if the user navigates to the site, then to the document library and goes down thru the folders. She won't see the folders on which she doesn't have any permissions. So, that means the user really doesn't have any kind of access.

any ideas?