I don't believe there is a Windows Event for a file move, out of the box. What you'd need is to find a 3rd party tool that would log these moves, and update a log file which you can point LEM at. There are a few such tools out there, and if you're a programmer look at using the FileSystemWatcher Class in .NET to knock up a custom program
But this won't help you in this case. I think you may have to accept the move, find and implement a tool that will log this in future, and be smug knowing next time you'll catch the culprit!