I've got the same problem - updater constantly trying to fetch the last file and restarting the process again and again for some reason. But restarting the updater even several times didn't help. I was able to continue upgrading by removing this last package (in my case it was a manually installed from .deb nexuiz-data package; "sudo lsof | grep http | grep /var/cache/apt" during fetching helped to identify it).
I've got the same problem - updater constantly trying to fetch the last file and restarting the process again and again for some reason. But restarting the updater even several times didn't help. I was able to continue upgrading by removing this last package (in my case it was a manually installed from .deb nexuiz-data package; "sudo lsof | grep http | grep /var/cache/apt" during fetching helped to identify it).