  Interference between CKM-favored b --> c ubar d and doubly-CKM-suppressed
bbar --> ubar c dbar amplitudes in final states used for B flavor tagging gives
deviations from the standard time evolution assumed in CP-violation
measurements at B factories producing coherent B0 B0bar pairs. We evaluate
these deviations for the standard time-dependent CP-violation measurements, the
uncertainties they introduce in the measured quantities, and give suggestions
for minimizing them. The uncertainty in the measured CP asymmetry for CP
eigenstates is ~2% or less. The time-dependent analysis of D*pi, proposed for
measuring sin(2 beta + gamma), must incorporate possible tag- side
interference, which could produce asymmetries as large signal asymmetry.
