Custserv advises that movement due to AB should not provoke AoOs from the one delivery the AB, but should provoke AoOs from other creatures. In this instance, I agree with custserv.
It is important to note that the rules, as written, would allow the AoO as all conditions required to create the situation occur (movement from a threatened square with no specific AoO exception). I just agree with custserv that they *should* have made an exception in this case.
From a logical perspective, it doesn't make much sense. You to hit a creature so hard that it flies back so slowly that you have time to get in a second attack?
From a balance perspective, it is a bit of a toss up. In some creatures, this would double their normal attacks per round which is a very large change in power. In others (big earth elementals), they would 'regain' their sacrificed attack in the form of an AoO which is a minor adjustment in power. In others, particularly outsides with this feat, it makes the feat a useful option, though still unlikely to be picked over a full attack when available. I tend to be cautious with power levels, so I favor the more restrictive approach and don't allow the AoO.