To elucidate the V-shaped switching reported by Inui Et al., we have studied another binary mixture. In its free-standing film, several subphases were observed in the ordinary sequence, indicating frustration between ferro-and antiferro-electricity; in particular, the antiferroelectric subphase exists in a temperature range as wide as 22 degrees C and the helical pitch is longer than 2.5 mu m. In a homogeneous cell, however, only two liquid crystal phases were distinguished; one is SA and the other is a phase characterized by the nearly V-shaped switching. We have concluded that the substrate interfaces induce tilting randomization, breaking the reduced intrinsic tilting correlation in adjacent layers.