Or at least it's very inconsistent. A lot of the times when hitting planes flying away, I see the flak detonating where it should but doing no damage to the planes. From what I've noticed it seems to affect the light and heavy AA guns. Haven't tested AA vehicles and fliegerfaust appears to be unaffected.
Should also note that I've only noticed this on pacific maps since the update since I haven't played the old maps since then.