gistfile1.txt

    mat4 old = uOldGeomMats[int(aGeomIndex)];
    mat4 new = uGeomMats[int(aGeomIndex)];
    mat4 final;

    float a = new[0][0];
    float b = old[0][0];
    
    // works :
    // final[0][0] = old[0][0];
    
    // works :
    // final[0][0] = new[0][0];
    
    //  warning X3206: implicit truncation of vector type :
    final[0][0] = new[0][0] + old[0][0];