  We study the evolution of linear density perturbations in the context of
interacting scalar field-dark matter cosmologies, where the presence of the
coupling acts as a stabilization mechanism for the runaway behavior of the
scalar self-interaction potential as in the case of the Chameleon model. We
show that in the "adiabatic" background regime of the system the rise of
unstable growing modes of the perturbations is suppressed by the slow-roll
dynamics of the field. Furthermore the coupled system behaves as an
inhomogeneous adiabatic fluid. In contrast instabilities may develop for large
values of the coupling constant, or along non-adiabatic solutions,
characterized by a period of high-frequency dumped oscillations of the scalar
field. In the latter case the dynamical instabilities of the field
fluctuations, which are typical of oscillatory scalar field regimes, are
amplified and transmitted by the coupling to dark matter perturbations.
