Ah, interesting question. On any multi-bolt c'sunk application, the true position of the holes becomes critical to get fastener bearing all the way around the bearing surface of the hole. There is also the fact that there is more of a tendency for the c'sunk parts to lose clamp load than a part with a 180 degree bearing surface as a result of the geometry of the c'sunk.
With those two things being said, actual fastener loosening by rotation is an extremely uncommon failure mode with Taptites. The zero clearance fit that you get when forming threads really keeps them from vibrating loose. I can't remember the last time I heard of a vibration loosening problem with a Taptite. I do get clamp load loss due to embedment, but that is independent of the Taptite thread.
