  Stochastic sandpiles self-organize to a critical point with scaling behavior
different from directed percolation (DP) and characterized by the presence of
an additional conservation law. This is usually called C-DP or Manna
universality class. There remains, however, an exception to this universality
principle: a sandpile automaton introduced by Maslov and Zhang, which was
claimed to be in the directed percolation class despite of the existence of a
conservation law. In this paper we show, by means of careful numerical
simulations as well as by constructing and analyzing a field theory, that
(contrarily to what previously thought) this sandpile is also in the C-DP or
Manna class. This confirms the hypothesis of universality for stochastic
sandpiles, and gives rise to a fully coherent picture of self-organized
criticality in systems with a conservation law. In passing, we obtain a number
of results for the C-DP class and introduce a new strategy to easily
discriminate between DP and C-DP scaling.
