Form renders twice for every parent update

Hello,

### Are you submitting a **bug report** or a **feature request**?

I am submitting a bug report.

### What is the current behavior?

The Form component renders twice for every update their parent makes. When logging all render props, nothing changes between the two renders.

### What is the expected behavior?

I would expect the Form component to only render once.

### Sandbox Link

On this [CodeSandbox](https://codesandbox.io/s/react-final-form-simple-example-forked-j0ksi?file=/index.js) which is the simple example from the docs, on initial render the Form renders twice.

### What's your environment?

CodeSandbox / latest versions of all packages

### Other information

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Thanks in advance!