We present an interesting phenomenon of the mechanically aligned monodomain state of polar nematic liquid crystals transforming into the polydomain one. This unusual transformation may result from mismatching of the dipolar vectors. By stretching or shear-flowing the polar nematic liquid crystal, the perfect orientation can be achieved with respect to the long molecular axis, but the misorientation exists with respect to the polar vector. After the prolonged annealing, then, the free energy of the molecules is minimized by producing new defects which satisfy the continuity of polar orientation, but lead to the loss of macroscopic molecular orientation.