  The one-dimensional Klein-Gordon equation is investigated with the most
general Lorentz structure for the external potentials. The analysis and
calculation of the reflection and transmission coefficients for the scattering
of particles in a square potential, with an arbitrary mixing of vector and
scalar couplings, reveal circumstances which conflict with the predictions from
nonrelativistic quantum mechanics. It is shown that such anomalous scatterings
are mediated by antiparticle bound states, even if the incident particles have
low energies. The analysis of bound states also reveals surprising results,
remarkable is the inhibition of the Schiff-Snyder-Weinberg effect due to the
presence of a scalar coupling.
