Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes of other orbital properties. The magnitude of the effect on particle orbits has important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravity of the gas and the host star. Although the results converge with resolution for fixed box dimensions, we find there exists no convergence of the response of the particles to the gravity of the gas against the horizontal box size, up to 16 disk scale heights. This lack of convergence indicate that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence.