SSH Certificates configured in System-->Certificates-->SSH do not appear in the "SSH certificate" field in Services-->Rsync-->Tasks-->Edit when Public key authentication is specified. Symptom occurs whether the key is Created or Imported in the ssh certificate page. Only available choice in the dropdown is "None", which is no choice at all.
Key is tested to be valid. Rsync Task is specified as Type=Remote, Mode=Pull, Source Server specified as user@ip:/<path>