changed
    float specular = max(0.0, dot(normalize(gl_LightSource[0].position + vec4(0.0, 0.0, 1.0, 0.0)), normalizedNormal));
to
    float specular = max(0.0, dot(gl_LightSource[0].position, normalizedNormal));

Calculation for specular value has to be done like in all other shaders with the unmodified unnormalized lightsource position. Otherwise the specular effect will have weird behaviour.