  We show with neutron diffraction that a single-crystal of potassium hydrogen
deuterium carbonate at room temperature, namely KH$_{0.76}$D$_{0.24}$CO$_3$, is
isomorphous with the KHCO$_3$ and KDCO$_3$ derivatives. Protons and deuterons
are not disordered particles located at definite sites and Bragg peaks are best
fitted with separate H and D sublattices. We propose a theoretical framework
for nonlocal observables and macroscopic states compatible with the crystal
field.
