Matt had a point, as far as I was concerned. I hadn't been seeing the symptoms until I checked that box. Acting on a hunch, I had the Resources folder in the Panorama application bundle open when I quit. I chose to save and quit, and these 3 library databases changed their modification dates.
Prior to quitting, those files had a modification date from yesterday afternoon, so as Kurt says, the issue was there all along, but the symptoms were masked, because it was saving without asking.
Trying to review three open files, which don't have windows, may explain the remaining symptoms.