As I'm just learning Pelican, Dirkjan Ochtman pointed out that I can have "fancy" URLs via the ARTICLE_PERMALINK_STRUCTURE setting. So the blog spam you are seeing is a result of my publishing the same two articles with two different URLs (fancy and non-fancy). My apologies for the noise.
And actually, I found ARTICLE_URL and ARTICLE_SAVE_AS to be the settings I wanted to use instead . My publishconf.py now looks like this :