Okay, problem's back. I experimented a little, and here's what I found out.
The Temporary Burn Folder is empty, but the desktop.ini file appears as 'files waiting to be burned to disk' for that drive. It appears even when I'm playing a DVD in that drive, and there's no need for anything to be burned.
When I delete the desktop.ini file from the 'files waiting to be burned to disk' folder, the Temporary Burn folder disappears from the Burn folder.
When I reboot the computer, both the 'files waiting to be burned to disk' message appears for the DVD drive, and Temporary Burn Folder reappears (with nothing in it!).
Windows 7 Home Premium.