When copying files, such as Microsoft Office documents with a sensitivity label, to an encrypted USB device, the DLP agent prompts you twice for a justification.
When uploading a file to the encrypted USB device, Microsoft intercepts the transfer.
This interception is considered a complete transfer.
Once the user accepts the MS prompt, a new transfer is created to finish the transfer to the USB.
This new transfer also triggers an agent pop-up.
So the user will see two agent pop-ups, one for each transfer.