when files are copied on the root directory of the flash drive, they are retained. when a directory with files are copied, and the flash dive is unplugged, the either all files within the directory are lost and a blank directory remains.
Or the whole of the directory disappears. one to notice is that after copying the files, when i click on the flash-drive in windows explorer, i can see them. when unplugged and replugged again on the same or different computer, they are gone.