Helper texts does not display well in input groups

[azmeuk]

Describe the issue

Current Behavior

If one input in a group has helper texts, they are displayed on the right side of the input instead of the bottom.

<label>Enter your domain
    <fieldset role="group">
      <input aria-describedby="domain-helper" aria-invalid="true" type="text" value="yolo">
      <small id="domain-helper">
        This is not a valid domain<br>This domain is not registered
      </small>
      <input id="submit" name="submit" type="submit" value="Check">
    </fieldset>
</label>

Expected Behavior

I would except the helper to be displayed as usual at the bottom of the input.

Reproduction URL

https://codepen.io/azmeuk/pen/emJZLQy