Delayed deletion of records

[kenichiro matsuda]

I use kilo version designate.

I delete a record with the api (Delete a record),
but sometimes deleted record exists in the api (List Records in a Domain) result.
In the re-check a little later, it did not exist in deleted records.

The reason for deletion delay has occurred, I think that it is in the execution method of update_status() of the designate-central.
By "cast ()" The following methods are used, update_status () has become an asynchronous execution.

  PoolManagerAPI.update_domain()
  MdnsAPI.poll_for_serial_number()
  PoolManagerAPI.update_status()
  CentralAPI.update_status()

In the above methods, why use "cast()"?