  In a recent paper (Phys. Rev. Lett. 102, 015301 (2009), arXiv:0810.3763)
Rousseau and Denteneer claim that an unconventional "super-Mott" (SM) phase is
realized by bosons trapped in an optical lattice close to a Feshbach resonance
with a molecular state. The supposed SM phase, observed via quantum Monte Carlo
(QMC) simulations of an atom-molecule Bose-Hubbard model, is an incompressible
phase developing spontaneous atomic/molecular supercurrents which are perfectly
anticorrelated. Here we show that the identification of this phase is based on
a misinterpretation of the estimators of superfluidity in QMC, which break down
in the presence of coherent atom/molecule conversion. Our conclusion is that
the supposed SM phase is in fact a fully normal insulator.
