A Copy is a partition clone. Write Changed Sectors Only applies if you are copying (cloning) to a partition that has already been copied to that position. It doesn't work on the first copy. Only subsequent copies. I suggest you create a full backup of a partition using the "Faster Changes Only Backups" option. Then create a Changes Only Backup of the same partition. You only need to use the "Faster Changes Only Backups" option with a Changes Only backup if you intend to create subsequent incremental backups. It's not needed if you want to create differential backups. But it is necessary with the Full backup.