  By using the field-antifield formalism, we show that the method of Batalin,
Fradkin, Fradkina and Tyutin to convert Hamiltonian systems submitted to second
class constraints introduces compensating fields which do not belong to the
BRST cohomology at ghost number one. This assures that the gauge symmetries
which arise from the BFFT procedure are not obstructed at quantum level. An
example where massive electrodynamics is coupled to chiral fermions is
considered. We solve the quantum master equation for the model and show that
the respective counterterm has a decisive role in extracting anomalous
expectation values associated with the divergence of the Noether chiral
current.
