  The classical antiferromagnetic Heisenberg model on the dodecahedron has been
shown to have three magnetization discontinuities in an external field. Here it
is shown that the highest-field discontinuity can be directly traced back to
the strong magnetization jump leading to saturation at the Ising limit, which
originates from the frustrated connectivity of the molecule. This discontinuity
survives up to the $XY$ limit and disappears just before the ferromagnetic
Ising interaction fully polarizes the spins. The two lower-field jumps of the
model result from the competition of discontinuities that emerge from the
magnetization plateau surviving away from the Ising limit.
