Hmmm… So I generated a new mobi file from the original HTML and it displayed the same problem. Then I commented out most of the ebook (except the relevant sections) and made another mobi which didn’t have the problem. Then I tried adding in more and more of the original HTML to try to find the point where the problem begins… after 10 or 15 tries, I’m back to the full text and no display issue (at least not in the Previewer app — I have to borrow a real Kindle to make sure it’s not there as well).
Weird. The problem was consistently present even after multiple edits to the HTML file — until I took most of the text out and then put it right back in.
Why would that matter???