lua slider widget - reset_callback

I’m using the slider widget and I would like to reset the value to default (in my case 0.0) when double-click. I suppose that reset_callback would do the trick, but it doesn’t actually. If I double-click on the slider, it is set to 0.0. Any hint, why it’s not working?

local slider_threshold = dt.new_widget("slider"){

   reset_callback = function(self)
        self.value = 0.5
   end,

  label = _("threshold"),
  soft_min = 0.0, hard_min = 0.0, soft_max = 1.0, hard_max = 1.0,
  step = 0.01, digits = 2
}

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Thanks, that’s only a typo. Not related to the reset_callback question. I edit OP to be more clear.