I thought that the pattern may be due to something with the controller card it was connected to, so I moved the drive to the onboard 2.0 connector and ran the scan again, and there was no pattern as before. I then moved it again to the onboard 3.0 connector, and got continous bad blocks indicated. It would appear that I have some problems in both controllers, but then again, when I scanned a regular HDD in my USB 3 docking station connected to the addon controller, I didn't get a pattern like that. I guess it just doesn't like flash drives too well.