  Recently the lifetime of the excited $^{2}P_{1/2}$-state of S$^-$ was
measured to be $503\pm 54$ s (B\"ackstr\"om et al. Phys. Rev. Lett. 114, 143003
(2015)). The earlier theoretical lifetime of $436$ s was clearly outside the
experimental error bars. To investigate this discrepancy we have performed
systematic and large-scale multiconfiguration Dirac-Hartree-Fock calculations
for this system. After including a careful treatment of correlation and
relativistic effects, we predict a well-converged value of $492$ s for this
lifetime, with an uncertainty considerably less than 1%, thereby removing the
apparent conflict between theory and experiment. We also show that this result
corresponds to the non-relativistic limit in the $LS$-approximation for the M1
transition within this $^2P$ term. We also demonstrate the usefulness of the
latter approach for $^2P$ transitions in O$^-$, Se$^-$ and Te$^-$, as well as
for analogous M1 transitions within $^2D$ terms in Ni$^-$ and Pt$^-$ ions.
