Is pressure the key to hydrogen ordering ice IV?

Hydrochloric-acid-doped ice IV prepared at increasing pressures leads to growing endotherms observed with ambient pressure calorimetry. The endotherms are irreversible suggesting three possible scenarios for their origins: (1) a weakly hydrogen-ordered counterpart of ice IV is formed, but ambient pressure favours hydrogen-disordered ice IV, (2) increased pressure creates increased strain within the crystal structure of the ice, which is released upon heating yielding the endotherms or (3) the endotherms are kinetic overshoot effects related to the underlying orientational glass transition. X-ray diffraction cannot distinguish between these scenarios. Recent controversies regarding the preparation of ice IV are also discussed.