That's an edge-case of the way that person's software preserves multiple spaces by force in browsers; it replaces the second of two spaces between sentences in

That's an edge-case of the way that person's software preserves multiple spaces by force in browsers; it replaces the second of two spaces between sentences in the source with a similar, non-breaking space. Use the `diff` command (if you're on a real OS) to compare; you'll see the two spaces are not actually duplicates of the same character code in the font used on that page.