Photonic heterocrystals are prepared by sandwiching films of self-assembled opal and force-assembled Langmuir-Blodgett colloidal crystals. Anomalously strong light scattering in conjunction with low,. reflectivity is observed with increasing angle of incidence in the spectral range of photonic bandgaps. The occurrence of light scattering at the interface has been assigned to the optical mode mismatch between the two types of photonic crystals. Photonic bandgap-related mechanisms of trapping the decaying photonic crystal modes at the interface are suggested.