If it has been fixed, it must have been in the last week or two... I flew on a pure AA trip a couple of weeks ago, and for both of the two segments outbound I was in group 6.
During the layover I looked up AA's policy on this, which states (as above) that MVPG should be in group 4, so I asked the gate agent about it and she icily informed me that yes, we have your AS number on file, and no, we won't change your boarding group.
On the way back, one segment was group 6 and the other, inexplicably, was group 5.