Steve, after this reply I am not going to waste any more time on this point, so you can have the last word if you wish.
You refer to the gear train and main spring drive mechanism - this is what drives the entire shutter - blades, as well as the flash sync. These last two are connected mechanically in a way which does not allow slippage or variation in the position of the blades at the point when the flash is triggered - unless, as I said before, the shutter is faulty. And I am not talking about general wear and tear, but a serious fault. Apart from this circumstance it is not possible for the flash to trigger before the blades reach the fully open position. Like it or not, this is a fact.
You keep on citing Stroebel, but nothing you have quoted is at all inconsistent with what I have been saying. Problems occur when the shutter begins to close before the flash has finished (and, yes, I know that flash output is not always a good approximation of a step function). This is true for all types of shutter, not just leaf shutters, and, contrary to your original reasoning, would be true even if the shutter were capable of opening or closing instantaneously. It is also rather obvious.
I can quite imagine the 3KJ packs you use would create a problem with speeds over 1/60th, but your advice related to electronic flash in general, without that qualification - a wholly unreasonable restriction. Furthermore, the problem has nothing whatever to do with the explanation you gave. Leaf shutters will indeed sync correctly at any speed, but sometimes a flash may be too long for the shutter speed selected - a point I made clear in my original post on this thread.
With that, I am out of here.