This is only going to bite people installing from one USB stick to another.  USB-connected drives wouldn't be affected, because they report an actual serial number from the disk; it's just USB sticks that often do not, since they are cheap.  I may be missing the correct scenario here, but it appears what you are describing is not likely to happen.

On Sun, Oct 16, 2011 at 10:36 PM, Juan Francisco Cantero Hurtado <iam@juanfra.info> wrote:
On Sun, Oct 16, 2011 at 11:29:27PM +0000, Justin C. Sherrill (via DragonFly issue tracker) wrote:
>
> Why are you installing from one USB stick to another?  The original image is
> bootable.  You can copy the initial image onto both.  I realize that's not
> the original task you were trying to do, but it would have less problems.
>

I know. I was only testing the speed of my usb stick with hammer and
I discovered the bug. My steps are only a example :)

Some users install the operating systems in usb disks and they will
have this problem. No only a bootable OS like in the usb images, I mean
people with a real systems (tens of GB) in usb disks.

SATA, IDE and SCSI disks have a unique identifier, the serial number.
The USB disks need also a unique identifier.