Is array mode working correctly?

Hi, I'm struggling to make array mode working correctly. I made this very simple example on codesandbox, which I brought code from tests for array mode on tanstack react-form and add console.log at form.Field for subField. Like the screenshot below, on first render, value is correctly set. But on second render, it became undefined and react warns me it is changing from controlled to uncontrolled. Is this an expected behaviour or bug? and if it were expected, what was going on under the hood? https://codesandbox.io/p/sandbox/recursing-davinci-gjrtv9?file=%2Fsrc%2FApp.tsx%3A38%2C33