Wow! That seems to be it.
I have no memory of ever toggling that checkbox, but it was off on my iMac and on for my MacBook.
Turning it off appears to have solved this.
Great work Michael, and thanks for persisting with this. I’ll add a note about this in the book.
I think that it would be best to put the note earlier in the book, the first time you ask the reader to open multiple windows then relaunch the app, in the “Working With Windows” chapter, because I was wondering about that myself until I finally reached the “Using Tables & Custom Views” chapter.
BTW, Apple poorly named that setting. It should be reversed and renamed to something like “Remember Window States Across Application Launches”, which would be on by default.