I have about 18 kinds of Kalanchoe and have observed that as plants mature, the scallop-edge ones develop more pronounced scalloping, if the light is bright enough. While inside over winter, in much lower light, some can start making rounded leaves with no scalloping on the edges. When that happens, the leaves also point down at the tip instead of up. I haven't observed that on K. millotii in particular, but put a pic of K. blossfeldiana doing it here:
