  DM--DE coupling can be a phenomenological indication of a common origin of
the dark cosmic components. In this work we outline a new constraint to
coupled--DE models: the coupling can partially or totally suppress the Meszaros
effect, yielding transfered spectra with quite a soft bending above
$k_{hor,eq}$. Models affected by this anomaly do not show major variation in
the CMB anisotropy spectrum and it is herefore hard to reconcile them with both
CMB and deep sample data, through the same value of the primeval spectral
index.
