  For many years modeling of double-mode pulsation of classical pulsators was a
challenging problem. Inclusion of turbulent convection into pulsation
hydrocodes finally led to stable double-mode models. However, it was never
analysed, which factor of turbulent convection is crucial. We show that the
double-mode behaviour displayed in the computed models results from incorrect
assumptions adopted in some of the pulsation hydrocodes, namely from the
neglect of buoyant forces in convectively stable layers. This leads to
significant turbulent energies and consequently to strong eddy-viscous damping
in deep, convectively stable layers of the model. Resulting differential
reduction of fundamental and first overtone amplitudes favours the occurrence
of double-mode pulsation. Once buoyant forces in convectively stable regions
are taken into account (as they should), no stable double-mode behaviour is
found. The problem of modeling double-mode behaviour of classical pulsators
remains open.
