Thanks, guys, for your support.
Yes, I'm sure I'm using
"Books/{author_sort}/{title}" as the send-to. I copy-and-pasted it directly to the post from Calibre.
Your explanation makes (some) sense regarding the shortening of the file path. Why hasn't Calibre upped the limit of the file path length with the times and sticks to the ol' FAT32 is a question in itself.
But that doesn't explain what's going on with that other book I gave as example. In fact, most of the tens of books are stored under some shelf name: Fiction, Non-Fiction, Reference, Chess, Comics.
I have no idea why or where that came from, and as I wrote above, deleting the book and re-adding it sends it right back to the wrong place.
Edit: As a side question/observation. I've looked at
the documentation, and it seems I should be able to use
shorten to control how shortening the full path works so that it won't chomp off the "Books" folder.