I think it happens if you mix special actor characters with normal pedestrian characters e.g the special ones are the main mission characters like Lance Vance, Diaz, Jezz Torrent and the other Love fist members, Colonel Cortez, Mercedez etc where as the normal characters are just the random pedestrians that walk around vice city. Also I dont think Tommy Vercetti counts as a special character.
EDIT: lol I just edited your post there by mistake and thought I was replying...