This is very confusing. I have a 32gb sd card inserted. I insert the USB flash drive and everything seems to be OK. When I unmount the USB drive the SD card is unmounted as well! I would have thought that in the bottom right of the screen there should be two icons one for usb and on for sd card. Is this a know challenge or operator error? How should I be unmounting the USB drive, which I want to do frequently, whilst leaving the SD card alone?