Trace to complex collision returns incorrect PhysicalMaterial

uint16 FTriangleMeshImplicitObject::GetMaterialIndex(uint32 HintIndex) const
{
#if 0
    if (MaterialIndices.IsValidIndex(HintIndex))
    {
        return MaterialIndices[HintIndex];
    }
#else
    int32 ExternalFaceIndex = GetExternalFaceIndexFromInternal(HintIndex/*InternalFaceIndex*/);
    if (ExternalFaceIndex > -1 && MaterialIndices.IsValidIndex(ExternalFaceIndex))
    {
        return MaterialIndices[ExternalFaceIndex];
    }
#endif
    // 0 should always be the default material for a shape
    return 0;
}