  We argue that superluminal propagation in a gravitational field discovered by
Drummond and Hathrell in the lowest order of perturbation theory remains intact
in higher orders. The criticism of this result based on an exact calculation of
the one loop correction to the photon polarization operator in the Penrose
plane wave approximation is not tenable. The statement that quantum causality
is automatically imposed by classical causality is possibly invalid due to the
infrared nature of the same triangle diagram which also contributes to the
quantum trace anomaly.
