It took me a bit to nail this down, but when I use AdSense Injector with Drigg, it prints out the injected code for the ad immediately prior to executing it. This could have been anything - an Ajax problem, a Digg module quirk, Filtered HTML filtering improperly - but I spotted this similar problem in a seemingly unrelated Drupal issue with the Garland theme:
And so I tried using the 4plus theme, and the problem disappeared. It's theme-based, and it's the default Drigg theme. You seem to have done a lot of work recently getting various media types embeddable in Drigg - posting a code snippet to help the default theme get along with AdSense Injector would be tremendous if you could.
The problem occurs in both full-page views and Teasers. And only in Drigg modules - in a Story, for example, it displays correctly even under the default theme.