  We revisit the sandpile model with ``sticky'' grains introduced by Mohanty
and Dhar [Phys. Rev. Lett. {\bf 89}, 104303 (2002)] whose scaling properties
were claimed to be in the universality class of directed percolation for both
isotropic and directed models. Simulations in the so-called fixed-energy
ensemble show that this conclusion is not valid for isotropic sandpiles and
that this model shares the same critical properties of other stochastic
sandpiles, such as the Manna model. %as expected from the existence of an extra
%conservation-law, absent in directed percolation. These results are
strengthened by the analysis of the Langevin equations proposed by the same
authors to account for this problem which we show to converge, upon
coarse-graining, to the well-established set of Langevin equations for the
Manna class. Therefore, the presence of a conservation law keeps isotropic
sandpiles, with or without stickiness, away from the directed percolation
class.
