This is more than likely due to downed cavalrymen having an indefinite position, not all people will run ragdoll physics, or if limited will not choose the downed cav as a ragdoll to save CPU power. The server will always run ragdoll's on everyone (I think), so theres a discrepancy between where the rider has been downed and where you see they have gone down. This is the reason some riders appear to have landed somewhere else, and then stand up 10 metres away. I think this could be related to you stabbing directly at the rider with no damage.