  We examine the conditions of validity for the Lifshitz-Matsubara sum formula
for the Casimir pressure between magnetic metallic plane mirrors. As in the
previously studied case of non-magnetic materials (Guerout et al, Phys. Rev. E
90 042125), we recover the usual expression for the lossy model of optical
response, but not for the lossless plasma model. We also show that the modes
associated with the Foucault currents play a crucial role in the limit of
vanishing losses, in contrast to expectations.
