Geographic Calculator measures most geodesic distances along the surface of the datum. However, with points containing Z values that refer to ellipsoidal heights, it is possible to measure distance along an ellipsoid that has been scaled to that height.
Inverse distance calculation using the geodesic method for points that contain ellipsoidal height values are calculated on an ellipsoid that has been expanded or contracted geocentrically to fit the source point height (first input).
Forward calculations on an input point that contains an ellipsoidal height use distance measured on an ellipsoid that has been expanded or contracted to the height of the input point.
To disable this advanced calculation, navigate to Options > Administrative Settings and go to the Geodetic Tab. Check the option Do not allow height above the ellipsoid Forward/ Inverse calculations. This will remove the fields for Height in the interactive Conversion job when calculating forward and inverse and on the Point Database Forward Inverse job.