Do they have the same VID/PID? Do they have serial numbers? Do they have different serial numbers?
Did you make the INF files? Have you been changing them during development?
I would try unplugging them both, deleting the specific entries in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Usb
Reboot, plug them in, check to make sure that they have the same drivers.
If it gets down to it use "graphedt.exe" or "graphedit.exe" to insert the "filter" and look at the property sheets.