After the High Detail update, the dragon mace's head became smaller. However, the special attack still looked like it had an old dragon mace head, and now looked like if there was empty space between the edge of the special attack's "aura" and the actual head of the dragon mace.
The dragon mace is actually a morning star, not a mace. A mace is a blunt object on the end of a short metal pole, or stick, whereas a morning star is a blunt object covered in spikes and attached to the end of a short pole. It possibly got its name because it looked like a mace, and calling it a "dragon morning star" would sound odd.