It was discovered on PTR earlier and now confirmed by the GC:  http://forums.worldofwarcraft.com/thread.html?topicId=19717353372&sid=1

The nerf to armor pen in 3.2.2 is intentional. Compared to the recent buff where we increased the value of armor rating to 125%, this nerf would take it back down to 110%. While we are still evaluating the effects of this change in the 3.2.2 build, we did want to let you know of the possibility in case you were about to spend a lot on armor pen gems.

In fact, this was really the point. Several melee specs (and Marksman hunters) had begun to focus on armor pen at the expense of all other stats. Gear without armor pen was being passed over and gem sockets were increasingly being filled with just this one stat. While every spec has stats that are more valuable than others, this one felt like it was starting to trump everything. Not coincidentally, characters stacking lots of armor pen were starting to do more damage than their peers and more damage than we were comfortable with.

This change is largely for PvE reasons, though we won't cry at all if melee damage in PvP drops a little as a result.

We're letting you know now so that this doesn't feel like a stealth nerf, assuming it goes live. While you might disagree or be frustrated by the change (though I also suspect it won't come as a surprise to many players), we ask that you try and keep your response to something appropriate for these forums.

So I guess this affects our rogues, feral druids, arms warriors, and blood dks.

I just wanted to touch a little on the rogue side of things.

Theorycrafting, in current projected BiS gear it was looking like we'd go Mace spec of all things stack all the ArP we can get, and start making use of a rupture-less cycle.    Heh, not the first time this was suggested and not the first time it was squashed before we can actually do it.

Anyways, that meant we'd drop rupture entirely and Evis spam all the way.   With enough Armor Pen and other BiS stats, Evis finally out did Rupture in efficiency.    Well, it would have been.

Now we'll have to re-calculate a few things, seeing if ArP is still worth it, or Agi might make a come back.    What I think is likely is that Blizz will never allow us to drop Rupture from our cycles.    If we find a way, they'll nerf it!  lol