Bug#814081: Fails to keep USB key unmounted

[Me]

Package: gnome-shell
Version: 3.14.4-1~deb8u1

Dear Maintainer,

I own a Kingston DataTraveler USB key. When I want to unplug it, I click
on the "Eject" button in GNOME Shell's notification bar.

The key is properly unmounted and disappears briefly from Nautilus, then
it is immediately mounted again, as if I just plugged it.

It annoys me because I can't be sure nothing is being written on the key
when I unplug it, which can lead to data loss.

I filed this bug for GNOME Shell because it doesn't happen with other
desktops (I tried with XFCE, MATE, Ubuntu with Unity, and even Windows
10). Unmounting from Nautilus works as it should, too. The 'eject'
command in a terminal works. It's really specific to GNOME Shell.

It happens only with this USB key : I have two other keys from other
brands and they are properly unmounted. I would assume it's just a bad
quality USB firmware if it didn't happen only in GS.

I can reproduce the bug on a fresh Jessie install.

My kernel version is 3.16.7-ckt20-1+deb8u3. I observe the bug on the
backported 4.3.0-0.bpo.1-amd64 kernel too.