What I am meaning is if for some reason the motors are tuned faster than the kernel will allow you often get issues. Normally this cant be done as Mach will not allow you to set the velocity faster than the kernel, that is selected, will allow. I have had this in simulations though as I use the SmoothStepper and have often brought my xml home for testing purposes and because I don't have a SS here (or didn't at the time) just set the xml to use the parallel port. If I recall I usually got a warning when first starting Mach and pressing the Reset that the motors were tuned too fast for the kernel.
Hood