It's lag. It takes time for their end to tell your end that they have bailed. When they bail out, the plane is still going in the last direction it went but it was sent some information that the plane is no longer alive. It changes to, typically, an open chute because lately the bandwidth or number of aircraft around you prevents the data to be sent in a steady stream and thus you don't see the aircraft disappear and the chute appear then open. You just see the aircraft become whole again, travel a few feet then change to an open chute.
-SW