Q:

USB 3.0 hard drives don't spin down when "safely removed" from Nautilus

I have a few external drives, some using external power, other being USB powered.
I plug my USB 3.0 drive in a USB 3.0 port.
When I "eject" the drive (from Nautilus) it keeps on spinning.
When I "remove safely" the drive, its name disappears from Nautilus, but the drive keeps spinning. I don't see the point.
I need to physically unplug the USB cable to stop it.  
How can I make a drive stop spinning when ejected?
Now, something weird is happening, that might help :
If I plug this same USB 3.0 drive in a USB 2.0 port, it will properly shutdown and stop spinning when I "remove safely" the drive.
Then when I plug it back to the usb 3.0 port, and try to "remove safely", it will... remount automatically! This is really weird, I don't get it.
Last thing I noticed is that the command udisks --detach /dev/sdb does the trick. Why would "remove safely" not do it?

A:

AFAIK, "Remove safely" just unmounts the device, and removes it from udev. It doesn't send any command to the drive to shut down.
On the contrary, udisks --detatch does so: (udisks manpage)
--detach device_file [--detach-options options]
       Detaches (e.g. powering down the physical port the device is
       connected to) the device represented by device_file using a
       comma-separated list of options.

