  We investigate two points related to existing treatments of isospin-breaking
corrections to the CVC relation between the e^+e^- --> pi^+ pi^- cross-section
and dGamma[tau^- --> nu_tau pi^- pi^0]/ds. Implications for the value of the
hadronic contribution to a_mu =(g-2)_mu /2 based on those analyses
incorporating hadronic tau decay data are also considered. We conclude that the
uncertainty on the isospin-breaking correction which must be applied to the tau
decay data should be significantly increased, and that the central value of the
rho-omega ``mixing'' contribution to this correction may be significantly
smaller than indicated by the present standard determination. Such a shift
would contribute to reducing the discrepancy between the tau- and
electroproduction-based determinations of the leading order hadronic
contribution to a_mu.
