Careful theoretical studies of the nuclear collective inertia based on the non-relativistic mean-field theory and the cranking model [N. El Aouad  et al., Nucl. Phys.  A676}, 155 (2000)] indicate that the moments of inertia of the super-deformed nuclei calculated using various standard methods and parameterizations exceed systematically  the experimental values. Similarly, but for other reasons the relativistic cranking calculations based on the relativistic mean field method present, in our opinion, a different class of systematic deviations from experiment. The origin and possible explanations of these deviations are discussed briefly.

PACS numbers: 21.60.--n, 21.60.Fw, 21.10.Pc, 21.30.--x