Adding subfiles to super is confusing. When I selected a subfile and clicked on add to superfile. I didn't check "append" and it throwed an error saying the file already exists which didn't make any sense because the file am trying to add is not in super. But when checked the "append" check box, it then added. By default, "append" check box should always be checked and I don't see any reason why we need the append check box unless am missing something.