If I have the [A:] drive enabled in the BIOS, and no device connected, then
a USB Floppy will NOT be found or assigned a Drive Letter.
If the [A:] drive is disabled, the USB Floppy is properly recognised at boot
time, assigned the A: Drive Letter wether or not a standard Floppy is
connected at the time.
This is how my system behaves, other's may have it differently, but I think
a modern OS is setting things up according to how BIOS enumerates hardware
as it is found at boot time.
If you don't have any standard Floppy, just try and disable it in the BIOS
setup!
Tony. . .