  We revisit the problem of the kink in the charge radius shift of neutron-rich
even lead isotopes. We show that the ability of a Skyrme force to reproduce the
isotope shift is determined by the occupation of the neutron 1i11/2 orbital
beyond N=126 and the corresponding change it causes to deeply-bound protons
orbitals with a principal quantum number of 1. Given the observed position of
the single-particle energies, one must either ensure occupation is allowed
through correlations, or not demand that the single-particle energies agree
with experimental values at the mean-field level.
