As you discovered, PingPlotter does a name lookup only once - when you start the trace.
PingPlotter is architected around the use of IP Addresses with related names. The names are informational only. This means that a change of the IP Address that a name is associated with won't change the IP at all - just as you've discovered.
There is no way to have PingPlotter realize the IP changed. To have this happen, there are some relatively significant internal changes that would need to happen. We are investigating that, but don't have a scheduled implementation for it.
