Disorder of stacking of vacant sites in the crystal structure of II₃V₂ compounds, including the diluted magnetic semiconductor (Zn_1-xMn_x)₃As₂ is investigated. Special attention is paid to the remanent disorder at temperatures much below the order-disorder phase transition temperature T_ph. Dependences of T_ph and the activation energy of hopping conductivity on composition are analysed. Good agreement is obtained between theory and experimental results for the phase transition and the hopping conductivity, occurring in two quite different temperature regions. It is suggested that the remanent structural disorder leads to generation of complex centres with a large magnetic moment and a large amount of internal spin degrees of freedom. We call these centres clusters of polarization. Conditions of freezing-in of a system of interacting clusters of polarization is analysed. A way to obtain the parameters describing these centres and their interaction is discussed.