"Revert to Saved..." grayed out in Tutorial song

The "Getting Started With Logic" guide often invites the reader to "Revert to Saved..."

However, the "Revert to Saved..." menu option is grayed out (when prompted to revert to saved, I just close and re-open the Tutorial song)

"Revert to Saved..." seems intuitive and reasonable enough (I've just made a mess of my song and now I'd like to undo everything and revert back to my originally saved song) - so what does it mean when it's grayed out?