Not sure if I saw this correctly but when playing my "guards" army (6 guards infantry, 2 guards cav, 2 light dragoons, 4 rifles, 2 grenadiers, 3 howitzers, 1 gen), I could've sworn I saw my guard infantry fire 1 volley by rank on incoming cav. I had 1 unit of rifles in skirmish in front but they shot their volley about 3sec. before I saw the volley in question.