Syskey on USB drive

Hi, i have used Syskey on Floppy for years on customer Laptops. In
january this year a customer wanted to use syskey (on XP) without a
floppy. I have used USBDLM for mounting the USB devices to the drive
letter A.
USBDLM: http://www.uwe-sieber.de/usbdlm_e.html
I configured, that a usb-drive with a specific name should always be
mounted to A, all others from G to J.
So you can make a backup to another usb-stick, change the name to force
the mount to A and use it in case of a broken or lost device.
My concern is:
if a usb-device is attached before a user is logged on to the machine
and this specific device was not plugged in bevore on this machine,
would it mount properly?
This problem occured a few days ago:
We used Pretec iDisk Diamond sticks. They are very small and handy. We
also used the type with 128MB, mainly for preventing to use the device
for other purposes as the logon process.
Now we had following issues:
The customer told me that he cannot log on to his laptop. The displayed
message tells "syskey not found on drive A. Please insert disk"
(Translation from german XP). I told him to use his backup-Stick (which
was created on the same machine a few weeks ago) and he was able to
logon. For investigation purposes i told him to plug in the "primary
stick". When he plugged it windows reacted like it was a
"new-and-never-bevore-plugged-in-device".
Messages with installing drivers and "device can now be used" appeared.
The next reboot, the "primary stick" worked again without problems...so far.
Any ideas what happened here?