I was looking for easy way of reporting an sub issue. After googling I have found the issue 8308 which describes how to do that. The thing is that clone button is not intuitive. It would make much more sense when the clone is placed into the section of related issues AND the default relationship is set to child of the issue. The title would be instead of clone something like "Report Related".

It is of course possible that there are much more usability cases where cloning makes more sense, then the clone can stay where it is today and report related is additional button with almost identical function.