According to the authors of Light Speed Variation From Gamma-ray Bursts[1], photons from gamma ray bursts show a speed dependency on their energy. Though inconsistent with current theories, the observations described in the paper are consistent with predictions of quantum-geometry dynamics and easily explained by it without violation of the speed of light.
Observed-Light-Speed-Variations-and-QGD
[1] http://arxiv.org/pdf/1607.03203v1.pdf