Yes, and when I edit the page I linked to in the original post I can see the plugin describing how the description will be displayed:
View post on imgur.com
And I can see the plugin generating its <head> elements on the page inside this comment block:
<!– All in One SEO 4.0.17 –>
metas etc here
<!– All in One SEO –>
But there is no <meta name=”description” in there (but it is there in more recent posts)