Light configuration on Shelly 1 Tasmota flashed

Tags: #<Tag:0x00007f739906f090> #<Tag:0x00007f739906ec58>

Hi, I had flashed the Shelly 1 with the latest tasmota firmware.
I had installed HA, configurated well the MQTT platform and the Entities “Light” in configuration.yaml:
mqtt:
broker: core-mosquitto
username: myuser
password: mypassword

light:

  • platform: mqtt
    name: Luceprova
    state_topic: stat/luceprova/POWER
    command_topic: cmnd/luceprova/power
    payload_on: ON
    payload_off: OFF
    retain: false

Now I have on the control panel the entity “Luceprova”, when I click the button the light comes on but the button automatically return on the off position (the light remain on!!).
To put off the light I have to press the button immediatly after, before it turns off automatically.
If I write
availability_topic: tele/luceprova/LWT the light becomes not avaible.
Please can anyone help me?
Thank you