I've given that a try. I created a parent category called "Articles", and a child category called "Arduino". I created a couple of test articles and put them in the "Arduino" category. If I set the Static Category block to look at the parent category of "Articles", I don't see any articles. If I set the Static Category block to look at the child category "Arduino", I do see articles.
Is there some other setting to allow the parent category to show the child category articles?
Also, when I do see the articles, I only see them when I'm logged in as admin, not as guest. I have set all the block, categories and articles to Access Settings -> Guests, Regular Members (basically copied the Welcome block's access settings).
Resolved. I tried this so many ways, I had forgotten to apply the view permission on the articles that time around. I still need to figure out why the categories won't show as above.
edit: completely fresh install of SMF 2.0.11 and PortaMX 1.54ecl. Nothing else installed.