  The approximate symmetry of the strong interactions under isospin
transformations is among the most precise tools available to control hadronic
matrix elements. It is crucial in extracting fundamental parameters, but also
provides avenues for the search of phenomena beyond the Standard Model. The
precision of the resulting predictions requires special care when determining
the quantities they are to be tested with. Specifically, in the extraction of
branching ratios often isospin symmetry is assumed at one point or another
implicitly, implying a significant bias for precision analyses. We extract a
bias-free value for the production asymmetry between charged and neutral $B$
meson pairs at $B$ factories and discuss its consequences for the determination
of branching fractions generally, and isospin-violating observables like the
rate asymmetries in B -> J/psi K or B -> K* gamma decays specifically.
