  Based on dynamical renormalization group (RG) calculations to the one-loop
order, the surface growth described by a nonlinear stochastic conserved growth
equation, {\partial h \over \partial t} = \pm \nu_2 \nabla^2 h + \lambda\nabla
\cdot (\nabla h)^3 + \eta, is studied analytically. The universality class of
the growth described by the above equation with +{\nu_2} (diffusion) is shown
to be the same as that described by the Edwards-Wilkinson (EW) equation (i.e.
+\nu_2 and \lambda=0). In contrast our RG recursion relations manifest that the
growth described by the above equation with {-\nu_2}(anti-diffusion) is an
unstable growth and do not reproduce the recent results from a numerical
simulation by J. M. Kim [Phys. Rev. E 52, 6267 (1995)].
