Comment on `Recombination induced softening and reheating of the cosmic   plasma'
  Leung, Chan & Chu (2004) claimed that a previously neglected reheating effect makes a small but noticeable change to the process of cosmological recombination. We revisit this effect by considering a system consisting of both radiation and ionizing gas under adiabatic expansion. In the thermal equilibrium limit, due to the huge radiation background, only a fraction about 10^-10 of the heat released from the recombination of atoms is shared by the matter. And in the standard hydrogen recombination calculation, the maximum fraction of energy lost by the distortion photons through multiple Compton scattering is certainly less than 10^-3. Thus this effect is negligible. 
Wan Yan Wong and Douglas Scott