Sorry for the inclarity. This only happens when I quit to the main menu from a game already in progress.
Debug log attached --- but on the face of it, the last instance of this issue isn't shown (11:21 PM today) so I'm not sure it'll be much help. Maybe it will, though; I can't reproduce on a fresh "load" of a game if I immediately quit. However, this has happened multiple times, always after longish play sessions.
Loading Items From Disk: 1 appears exactly as any other loading text for this game would. It is not a special Windows error window.
On a whim, I tested a suggestion that someone else had for a similar bug for this game, but ALT-TAB back and forth doesn't trigger this.