I have a Windows 7 or Vista computer that was backed up onto an external drive (WD Passport) using Windows Backup & Restore every week for almost a year. Now I am viewing these files on a Windows 8 computer. They are represented by a set of .zip files, that, according to the official documentation, store every file that has changed since the last backup, or for the first backup, obviously the entire drive. At the end of most "backup sets" is a .zip folder that is 22 bytes, or 1 kilobyte "on disk." However, when I open it, it is empty, it has no files or folders in it. Also, the last file is not at the end of every single "backup set," just most of them.
My questions are: (1) Why is it there and what does it hold? (2) Can I delete it without any problem? (3) If not, how about the last .zip in "backup sets" that don't have an empty .zip at the end? (4) Why is the last file empty only in some "backup sets," not all?