  For two-electron diatomic molecules, we investigate magnetic field effects in
non-sequential double ionization where recollisions prevail. We do so by
formulating a three-dimensional semi-classical model that fully accounts for
the Coulomb singularities and for magnetic field effects during time
propagation. Using this model, we identify a prominent signature of non-dipole
effects. Namely, we demonstrate that the recolliding electron back-scatters
along the direction of light propagation. Hence, this electron escapes opposite
to the direction of change in momentum due to the magnetic field. This is in
striking contrast to strongly-driven atoms where the recolliding electron
forward-scatters along the direction of light propagation. We attribute these
distinct signatures to the different gate that the magnetic field creates
jointly with a soft recollision in molecules compared to a hard recollision in
atoms. These two different gates give rise, shortly before recollision, to
different momenta and positions of the recolliding electron along the direction
of light propagation. As a result, we show that the Coulomb forces from the
nuclei act to back-scatter the recolliding electron in molecules and
forward-scatter it in atoms along the direction of light propagation.
