  It is shown that the so-called generic instabilities that appear in the
framework of relativistic linear irreversible thermodynamics, describing the
fluctuations of a simple fluid close to equilibrium, arise due to the coupling
of heat with hydrodynamic acceleration which appears in Eckart's formalism of
relativistic irreversible thermodynamics. Further, we emphasize that such
behavior should be interpreted as a contradiction to the postulates of linear
irreversible thermodynamics (LIT), namely a violation of Onsager's hypothesis
on the regression of fluctuations, and not as fluid instabilities. Such
contradictions can be avoided within a relativistic linear framework if a
Meixner-like approach to the phenomenological equations is employed.
