Using a new Win8 Dell laptop I copied some large files from USB3<->eSATA connected drive to the USB3 connected passport. These were fine. Later, I connected to a Win7 via USB2, using the USB3 cable supplied with the drive, copied about 20 GB of files, powered down and removed the drive. On the Win8 Dell, the added files did not show up. Back on the Win7 PC, they do. On both PCs the unused byte count is the same.