Hi Bob,
I have not faced this situation but, had some thing related to USB devices.
I have posted at List of USB Devices used
Your case may be helpful in verify my observation,
Can you please parse the event logs and search the USB devices serial number you have , then you may be able to discover how many times times a USB device plugged in to the PC,
I discovered it once and posted in forum but did not got any comment,
Your situation may validate my observations.
Regards