  There have been some recent claims in the literature about large right-handed
sneutrinos contributions to lepton flavor violating observables like $\mu \to
3e$ or $\mu - e$ conversion in nuclei in supersymmetric low-scale seesaw
models. These large contributions originate from $Z$-penguin diagrams which
show a much weaker dependence on the heavy masses than the photonic
contributions. We have traced this to an error in the evaluation of the
corresponding loop amplitudes which has propagated in the literature. We
explicitly show that after correcting this mistake the $Z$-penguins show the
expected decoupling behavior. Moreover, the reported dominance of the
$Z$-penguin over the photonic contributions disappears as well.
