For anyone stumbling across this in the future…
I’ve updated the example with the four cases on one page, including a detailed explanation of what happens (and why) in each of the four cases.
git clone --single-branch -b hugo-forum-topic-14929 https://github.com/jmooring/hugo-testing hugo-forum-topic-14929
cd hugo-forum-topic-14929
hugo server
It’s a 10 minute read, but worth the effort.