Impossible to turn off mqtt light after changing entity name in frontend

[bieniu]

Home Assistant release with the issue:
0.84.2

Last working Home Assistant release (if known):
Not sure, 0.83.x or 0.82.x

Operating environment (Hass.io/Docker/Windows/etc.):
Raspbian/Python 3.6/virtual_env

Component/platform:
mqtt/light

Description of problem:
Changing the name of the light entity in the frontend makes it impossible to turn off that light. After turn off the light, it stays in HA on.

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

light:
  - platform: mqtt
    name: 'Sonoff Basic 1740'
    command_topic: 'homeassistant/light/sonoff-1740/cmnd/power'
    state_topic: 'homeassistant/light/sonoff-1740/stat/POWER'
    availability_topic: 'homeassistant/light/sonoff-1740/tele/LWT'
    unique_id: 'sonoff-1740'
    payload_available: 'Online'
    payload_not_available: 'Offline'
    payload_on: 'ON'
    payload_off: 'OFF'
    qos: 1
    retain: true

Additional information:
Reproduce the issue:

1. Changing the name of the entity of mqtt light using the frontend
   
2. Turning off the light of the newly created entity in the frontend
3. The light will stay on.
4. After the HA restart, the light works correctly.

[emontnemery]

The same issue exists for other components (tested with switch.mqtt), and also if the entity has been autodiscovered instead of added manually.