  An earlier paper presented the potentially significant discovery that
disturbances in simplified simulations of a stellar disc model that was
predicted to be stable in linear theory grew to large amplitude over a long
period of time. The ultimate appearance of true instabilities was attributed to
non-linear scattering by a succession of collective waves excited by shot noise
from the finite number of particles. The paper concluded that no finite number
of particles, however large, could mimic a smooth disc. As this surprising
finding has been challenged as an artifact of the numerical scheme employed, we
here present a new calculation of the same model using a different grid
geometry that confirms the original behaviour.
