Hi,
just a guess, but do you have THC?
THC usually works an an 'overload axis'. This means that the Z axis works normally, but the THC height variations are applied to a mythical extra Z axis motor which
works in parallel with the main Z axis motor. In practice the up/down signals are sent to the main Z axis motor, but the idea remains that there are two sources of pulses,
the regular Mach generated Z axis trajectory pulses AND the THC pulses.
Mach can and does keep track of the main Z axis pulses but it cannot keep up with the overload axis. When you go do do a regular job the accumulated overload axis movement will offset
the Z axis. If you had Homed before then the accumulated overload offset would be accounted for and Mach would not dive into the table.
Craig