  Employing very simple electro-mechanical principles known from classical
physics, the Kibble balance establishes a very precise and absolute link
between quantum electrical standards and macroscopic mass or force
measurements. The success of the Kibble balance, in both determining
fundamental constants ($h$, $N_A$, $e$) and realizing a quasi-quantum mass in
the 2019 newly revised International System of Units, relies on the perfection
of Maxwell's equations and the symmetry they describe between Lorentz's force
and Faraday's induction, a principle and a symmetry stunningly demonstrated in
the weighing and velocity modes of Kibble balances to within $1\times10^{-8}$,
with nothing but imperfect wires and magnets. However, recent advances in the
understanding of the current effect in Kibble balances reveal a troubling
paradox. A diamagnetic effect, a force that does not cancel between mass-on and
mass-off measurement, is challenging balance maker's assumptions of symmetry at
levels that are almost two orders of magnitude larger than the reported
uncertainties. The diamagnetic effect, if it exists, shows up in weighing mode
without a readily apparent reciprocal effect in the velocity mode, begging
questions about systematic errors at the very foundation of the new measurement
system. The hypothetical force is caused by the coil current changing the
magnetic field, producing an unaccounted force that is systematically modulated
with the weighing current. Here we show that this diamagnetic force exists, but
the additional force does not change the equivalence between weighing and
velocity measurements. We reveal the unexpected way that symmetry is preserved
and show that for typical materials and geometries the total relative effect on
the measurement is $\approx 1\times10^{-9}$.
