During photon tracing, shadow shaders are not processed. This prevents light sources from casting shadows on objects twice (once through the shadow shader and once via transmitted photons), resulting in incorrect illumination.
Additionally, photons cannot mimic some Maya features such as a depth limit on shadow rays.
During the photon tracing phase, some view-dependent information (filter sizes, which are used in the bump and almost all texture nodes) is not available. You should turn off view-dependent filtering in all these nodes by setting Filter to zero and Filter Offset to a small positive value.