I was calibrating the X, Y and Z axis today and came upon an unexpected result.  I set the Z axis to a preset height and set Z to zero, also set X and Y to zero.  Entered -50mm into the move box and carried out the calibration move to the waste board surface.  Distanced moved was 50mm, so calibration a success.  Clicked on the GOTO Zero box on the Program Run tab and watched as the spindle went from -50mm back to zero but then kept moving in the positive direction until the upper Z limit switch activated.

Why didn't the Z stop when reaching +0.0000

Is there a setting that is incorrect?