Planck scale still safe from stellar images

The recent paper of Lieu and Hillman [1] that a possible, (birefringence like) phase difference ambiguity coming from Planck effects would alter stellar images of distant sources is questioned. Instead for {\em division of wavefront} interference and diffraction phenomena, initial (lateral) coherence is developed simply by propagation of rays (cf. van Cittert-Zernike theorem). This case is strongly immune to quantum gravity influences that could tend to reduce phase coherence. The phase ambiguity, if actually present, could reduce any underlying polarization of the light rays.