core: imap_email_content set to unknown after 30 seconds

The problem

I know there was a breaking change in 0.110.0, that imap_email_content should be set to unknown, when there is no email found. But the way it works (at least with Gmail) is, that the sensor sets its value correctly after receiving the email, but after 30 seconds it sets its status to an unknown, even then the email still sits in the inbox. So the sensor is basically useless, it has unknown value all the time except for 30 seconds after receiving the email.

Environment

Home Assistant Core release with the issue: 0.110.0
Last working Home Assistant Core release (if known): 0.109.0
Operating environment (Home Assistant/Supervised/Docker/venv): Ubuntu 19.10/Docker
Integration causing this issue: imap_email_content
Link to integration documentation on our website: https://www.home-assistant.io/integrations/imap_email_content/

Problem-relevant `configuration.yaml`

sensor:
  - platform: imap_email_content
    name: Alarm
    server: imap.gmail.com
    port: 993
    username: !secret gmail_username
    password: !secret gmail_password
    senders:
      - !secret alarm_email
    value_template: "{{ subject.split('Alarm - ')[1] }}"