Just to comment a bit further, I've been noodling over why the problem went away for me, and what I assume is that I probably still have the problem with the A axis, but since I went to servo motors and then better servo drives, the issue has not been able to manifest because the motors get a little behind during the 'instant' accell, but catch up within a tiny amount of movement, and most likely before the cutting tool touches the workpiece, so there is no practical effect.
If I recall correctly, I read somewhere that you are using Gecko drives. They have only a tiny error allowance and not much power (for a big motor), so they are unable to tolerate the error created by the slammed motor.
Be nice to have it fixed in any case . . . .
While I have your attention, Ray, let me repeat my appreciation for the great manual you have produced. Only used it a couple times, but even then it has saved me a lot of time and hassle.