  We consider the relaxation of a uniform current in a planar 2D conductor with
account taken of electromagnetic retardation effects. If the 2D conductivity is
larger than the speed of light, the straightforward solution for an infinite
plane gives a negative relaxation rate. However if one starts from a conducting
cylinder of finite radius and then increases it to infinity, the relaxation
rate just tends to zero while remaining positive. We suggest that recent
unusual plasmon-dispersion curves obtained by V. A. Volkov and A. A.
Zabolotnykh [arXiv:1605.00430] result from the incorrect finite-to-infinite
transition.
