"also_notifies" section is not purged by designate when removing it from "pools.yaml" file

The "also_notifies" section is not purged by designate when removing it from the "pools.yaml" file. Once it is added, it stays forever, and can only be updated. Below is an output from fresh installation and attached are full designate logs.

TRY 1 (section is not present; fresh installation):

# cat /etc/designate/pools.yaml
- id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
  name: default
  nameservers:
    - host: 10.130.194.93
      port: 53
  targets:
    - type: bind9
      masters:
        - host: 10.130.194.187
          port: 5354
      options:
        host: 10.130.194.93
        rndc_host: 10.130.194.93
        rndc_key_file: /etc/designate/rndc.key

# designate-manage pool show_config
...
Pool Configuration:
-------------------
also_notifies: []
attributes: {}
id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
name: default
nameservers:
- host: 10.130.194.93
  port: 53
ns_records: []
targets:
- masters:
  - host: 10.130.194.187
    port: 5354
  options:
    host: 10.130.194.93
    rndc_host: 10.130.194.93
    rndc_key_file: /etc/designate/rndc.key
  type: bind9

TRY 2 (section is added):

# cat /etc/designate/pools.yaml
- id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
  name: default
  nameservers:
    - host: 10.130.194.93
      port: 53
  targets:
    - type: bind9
      masters:
        - host: 10.130.194.187
          port: 5354
      options:
        host: 10.130.194.93
        rndc_host: 10.130.194.93
        rndc_key_file: /etc/designate/rndc.key
  also_notifies:
    - host: 10.130.194.93
      port: 53

# designate-manage pool show_config
...
Pool Configuration:
-------------------
also_notifies:
- host: 10.130.194.93
  port: 53
attributes: {}
id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
name: default
nameservers:
- host: 10.130.194.93
  port: 53
ns_records: []
targets:
- masters:
  - host: 10.130.194.187
    port: 5354
  options:
    host: 10.130.194.93
    rndc_host: 10.130.194.93
    rndc_key_file: /etc/designate/rndc.key
  type: bind9

TRY 3 (section is removed):

# cat /etc/designate/pools.yaml
- id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
  name: default
  nameservers:
    - host: 10.130.194.93
      port: 53
  targets:
    - type: bind9
      masters:
        - host: 10.130.194.187
          port: 5354
      options:
        host: 10.130.194.93
        rndc_host: 10.130.194.93
        rndc_key_file: /etc/designate/rndc.key

# designate-manage pool show_config
...
Pool Configuration:
-------------------
also_notifies:
- host: 10.130.194.93
  port: 53
attributes: {}
id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
name: default
nameservers:
- host: 10.130.194.93
  port: 53
ns_records: []
targets:
- masters:
  - host: 10.130.194.187
    port: 5354
  options:
    host: 10.130.194.93
    rndc_host: 10.130.194.93
    rndc_key_file: /etc/designate/rndc.key
  type: bind9

TRY 4 (section is re-added and updated):

# cat /etc/designate/pools.yaml
- id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
  name: default
  nameservers:
    - host: 10.130.194.93
      port: 53
  targets:
    - type: bind9
      masters:
        - host: 10.130.194.187
          port: 5354
      options:
        host: 10.130.194.93
        rndc_host: 10.130.194.93
        rndc_key_file: /etc/designate/rndc.key
  also_notifies:
    - host: 8.8.8.8
      port: 53

# designate-manage pool show_config
...
Pool Configuration:
-------------------
also_notifies:
- host: 8.8.8.8
  port: 53
attributes: {}
description: Pool genergated by Juju
id: 794ccc2c-d751-44fe-b57f-8894c9f5c842
name: default
nameservers:
- host: 10.130.194.93
  port: 53
ns_records: []
targets:
- masters:
  - host: 10.130.194.187
    port: 5354
  options:
    host: 10.130.194.93
    rndc_host: 10.130.194.93
    rndc_key_file: /etc/designate/rndc.key
  type: bind9