I once unmounted an USB device using Ubuntu or Debian file manager, and when the icon next to the drive that shows it is mounted disappeared I immediately pulled the USB device out. Turns out that Linux was still writing some data on the USB device on the time I pulled it out. Is this a file manager specific question? Can this happen when you unmount via command-line, too, or does the shell block until the device is save to pull out?
How to check if unmount of USB device is completed?
linux;usb device