  Solar and KamLAND data are in slight tension when interpreted in the standard
two-flavor oscillations framework and this may be alleviated allowing for a
non-zero value of the mixing angle theta_13. Here we show that, likewise,
non-standard flavor-changing interactions (FCI), possibly intervening in the
propagation of solar neutrinos, are equally able to alleviate this tension and
therefore constitute a potential source of confusion in the determination of
theta_13. By performing a full three-flavor analysis of solar and KamLAND data
in presence of FCI we provide a quantitative description of the degeneracy
existing between theta_13 and the vectorial coupling eps_e\tau^dV
characterizing the non-standard transitions between nu_e and nu_tau in the
forward scattering process with d-type quarks. We find that couplings with
magnitude eps_e\tau^dV ~ 10%, compatible with the existing bounds, can mimic
the non-zero values of theta_13 indicated by the latest analyses.
