After shutdown I notice that both the USB hub and the external USB drive remain active (lights on): the next time I try to boot the system hang after grub and I have to do a hard reboot. After that the system boots fine, until the next shutdown/boot cycle.
Ideas on how to troubleshoot/resolve the issue?
EDIT: The USB hard drive is powered by an adapter, while the hub is self powered; it's a dual-boot machine, with Windows XP on another partition and with Win there's no such a problem.
EDIT #2: It's a PC, and the USB devices remain active after the PC's shtudown: I mean, when the pc is completely off, not standby, not hibernated and not suspended. After that the CPU, PSU, GPU and the various fans are completely quiet.
EDIT #3: The problem occurs also if a SD card is in the reader at boot time.