  The Lorentz-violating model proposed by Myers and Pospelov suffers from a
higher-derivative pathology due to a dimension-5 operator. In particular, its
electromagnetic sector exhibits an spectrum which contains, in addition to an
expected massless photon, ghost contributions that could (in principle) spoil
the unitarity of the model. We find that unitarity at tree-level can be assured
for pure spacelike, timelike and lightlike background four-vectors (the last
two under restrictions upon the allowed momenta). We then analyze the
non-relativistic interparticle potential energy behavior for different
background four-vectors and compare to the usual Coulomb potential.
