Open layout setup and clear the check box named "Delineate..."
You are a magical person. I've been staring at [and, yes, I did RTFM] for weeks now. I would have had no idea that this check box had anything to do with this problem save for your note just now. I'm not even sure I would know what to search for.
Thank you for bailing me out yet again.
It was and still is a very irritating layout feature. For most list view layouts, I have to clear this box that always defaults to selected on a new layout. That irritation is what enables me to remember it.