  It is well known that the Solar System is presently moving through a
partially ionized local interstellar medium. This gives rise to a counter-flow
situation requiring a consistent description of behaviour of the two fluids --
ions and neutral atoms -- which are dynamically coupled by mutual charge
exchange processes. Solutions to this problem have been offered in the
literature, all relying on the assumption that the proton fluid, even under
evidently nonequilibrium conditions, can be expected to stay in a
highly-relaxated distribution function given by mono-Maxwellians shifted by the
local proton bulk velocity. Here we check the validity of this assumption,
calculating on the basis of a Boltzmann-kinetic approach the actually occurring
deviations. As we show, especially for low degrees of ionization, $\xi \le
0.3$, both the H-atoms and protons involved do generate in the heliospheric
interface clearly pronounced deviations from shifted Maxwellians with
asymmetrically shaped distribution functions giving rise to non-convective
transport processes and heat conduction flows. Also in the inner heliosheath
region and in the heliotail deviations of the proton distribution from the
hydrodynamic one must be expected. This sheds new light on the correctness of
current calculations of H-atom distribution functions prevailing in the inner
heliosphere and also of the Lyman-$\alpha $ absorption features in stellar
spectra due to the presence of the hydrogen wall atoms. Deviations from
LTE-functions would be even more pronounced in magnetic interfaces, which via
CGL-effects cause temperature anisotropies to arise.
