Custom component inside field does not receive focus

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

Bug report

### What is the current behavior?

I am embedding a react-autosuggest component inside a `Field`. When the field receives focus, the autosuggest component does not drop down to show the suggestions.

### What is the expected behavior?

When the field receives focus, the autosuggest component should drop down to show the suggestions.

### Sandbox Link

https://github.com/nareshbhatia/form-lib-demo

In the screenshot, notice the two Time Zone fields side-by-side near the bottom-right. The first is inside a `` and the second is raw (see code for both [here](https://github.com/nareshbhatia/form-lib-demo/blob/master/src/features/final-form-page/book-form.js#L193-L211)). The first one doesn't work, the second one works. The code for the embedded `Tz` component is [here](https://github.com/nareshbhatia/form-lib-demo/blob/master/src/features/final-form-page/components/tz.js).

### What's your environment?

final-form: 4.9.1
react-final-form: 3.6.5