Then I have a sort of pet theory. I was waiting for confirmation there, I've been nursing it since yesterday.
Put simply, Google is rethinking how Google+ relates to SEO in dramatic ways. Little by little they've nofollowed nearly everything that could pass authority. Now they've got a nofollow link associated with a hidden dofollow link replacing the single dofollow link. I'm thinking that Google is going to stop treating Google+ backlinks as normal backlinks, and develop a 'social backlink' system that thwarts at least the current group of blackhat SEO's from running up backlinks from this high authority site. The lack of a true API has made this inherently more difficult, but I'm guessing they've figured out how to mass automate this in some circles.
They may not be using this for anything yet, but they may be able to scan for this type of 'hidden link' and integrate its effect into Search differently. There are a lot of possibilities for how they could use this, and it could even improve certain things. It simultaneously could wipe out all attempts to use Google+ posts as a traditional internet backlink system (like dofollow links in forum comments), and help usher in a true 'Social SEO' era.