SlaveStatus Master_Server_Id does not reset with CHANGE MASTER

The Master_Server_Id show by SHOW ALL SLAVES STATUS keeps its old value after a CHANGE MASTER TO-command. It seems the value is only updated once the slave connects to the new master. This can be confusing if the history of the slave is not known and the IO Thread is "Connecting". In that case it's not immediately obvious if the Master_Server_Id shown is the ID of the current master server (temporarily disconnected) or of a previous master. It would be clearer if a CHANGE MASTER automatically assigned -1 or 0 to Master_Server_Id.