react-hook-form: [Bug] Hidden input is ignored, when another input with `register()` is present

Hidden input is ignored, when another input with register() is present 🐞

To Reproduce

1. Go to https://codesandbox.io/s/distracted-payne-1ooyh?file=/src/App.js
2. Click on Submit
3. Expected: In console check a submit object: test[0].validation has to be present with value false. Current: validation field is missing.
4. Select any value in <select> dropdown
5. Expected: In console check a watch object: test[0].validation has to be present with value true. Current: validation field is missing.

Codesandbox link https://codesandbox.io/s/distracted-payne-1ooyh?file=/src/App.js

• Version: checked 6.5.3 and 6.6.0

Additional context Removing from code

<input
     defaultValue={fields[index].required}
     ref={register()}
     name={`test[${index}].required`}
     type="text"
/>

helps to solve onChange issue. But a default value is still ignored and empty.