An explanation is presented for the temperature dependence of the fourfold intensity peak splitting found recently in the diffuse x-ray scattering from the disordered alloy. The wavevector and temperature dependence of the self-energy is identified as the origin of the observed behaviour. Two approaches for the calculation of the self-energy, the high-temperature expansion and the -expansion, are proposed. Applied to the alloy, both methods predict an increase of the splitting with temperature, in agreement with experimental results.