I wonder if it has something to do with the design of the barrel lug. I don't know a great deal about semi-autos (or any type of pistol for that matter), but it would seem to me that the up-and-down rocking motion of the barrel during firing may be contributing to (or the cause of) the dislodged take-down pin. The video I have seen (posted by another forum member) definitely shows the take-down spinning counterclockwise as it is working it's way out of the frame. Not that the barrel shouldn't be rocking upward during firing, but perhaps the shape of the barrel lug combined with the rocking motion is setting that take-down pin spinning loose. Anyway, it's just a thought.