Comment on SEO AdSense WordPress Theme by Erik.
Update: Interestingly, the problem seems to just be with the “Smart sizing” responsive ad (the code you gave as an example above). Right before you save and copy code, Adsense gives two options for responsive unit code, their “recommended” Smart Sizing and Advanced which say “code modification required”.
I just created and tested an “Advanced” responsive ad, which requires modifying the ad size you wish displayed to the device width. The code it generates gives you 3 sizes: 1) width: 320px; 2) min-width: 500px, and 3) min-width: 800px. Each width has a suggested corresponding ad size/shape which you can change.
So this Advanced ad version seems to work fine in a Stallion text widget. So why the Smart Sizing responsive unit doesn’t work is still a mystery.
(As an aside, I am wondering if one version is preferable over the other; the Smart Sizing is obviously easier to set up, though you can control the type of ad you want displayed based on a given screen size using the Advanced units. Taking that further, I could see someone setting up the 160×600 skyscraper sidebar ad unit to become a large rectangular ad once it goes into responsive mode (below say min-width: 500px or 480px), since that sidebar ad drops to the bottom of the wider main content column. A 300×250 or 250×250 ad might fill that space below the main content more completely and neatly than the thinner 160px width skyscraper. Just thinking out loud :) )