The Boltzmann-like kinetic equations for neutrinos interacting with a neutrino background were established in the early 1990s and used in early universe calculations. They are now being used in Supernovae calculations, but the validity of the equations has been questioned on the basis of a model calculation. I describe these concerns and demonstrate that, within this model one obtains incoherent time evolution which is entirely driven by the two neutrino correlations. I argue that this breakdown of the Boltzmann single particle behaviour is a pathology of the model, and may not apply in more realistic cases.
