We propose a model for the poling-inhibiting action of proton-exchange, associated to nonuniform fields induced in the crystal by the vanishing of ferroelectricity in the beta-phase of HxLi1-xNbO3. Predictions are corroborated by experimental results on the poling of 0.5 mm thick congruent LiNbO3 substrates with periods around 8 mu m, yielding regular bulk domain structures with aspect ratios as high as 250. (C) 2011 American Institute of Physics. [doi:10.1063/1.3571559]