Detailed study of a neutron Laue diffraction in a noncentrosymmetric crystal was carried out using a prototype of the experimental setup to measure the neutron electric dipole moment (nEDM) by Laue diffraction method (LDM). A new kind of spin rotation effect was observed for the first time. We attribute this effect to a difference of the two Bloch waves amplitudes in the crystal, which is caused by the presence of the definite small crystal deformation. In a revised scheme of the experiment, this effect could be exploited for a purposeful manipulation of the Bloch waves. © 2008 World Scientific Publishing Company.