It's NOT a CV bug!
I just did an interesting test - I wrote a simple test program that does:
Short, 2-axis linear move to initial position at 100 IPM
Short, 3-axis linear move to second position at 5 IPM
Repeat the above two moves in reverse, ending up back at the start position
This is run in a loop, and works perfectly every time.
I then replaced the two 3-axis linear moves with a helical move between the same two points, at the same feedrate
This faults the Z servo every time.
I then set the Z acceleration as low as Mach would allow (~0.2), and put an oscilloscope on the Z axis STEP line. Running the first test, I see a nice acceleration over the first ~0.5 second of the Z move. Running the second test, the step rate goes instantly from 0 to 10kHz - NO acceleration ramp at all! But it does appear to do a proper deceleration at the end of the move!
Note that the behavior is exactly the same, whether I run in CV or ExactStop mode, so it's NOT a CV problem.
Regards,
Ray L.