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**Do you want to request a *feature* or report a *bug*?**
Not sure if its a bug or a feature request.

**What is the current behavior?**
The component given as a fallback to Suspense is remounted each time a lazy child resolves.

https://codesandbox.io/s/z6v6x3n1np
This example shows how a fallback component, which counts up, is mounted more than once.

**What is the expected behavior?**
The fallback is mounted once and is only unmounted when all lazy children are resolved.
In the example the counter would run up to 9.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
react@16.6.0

);
    expect(ReactNoop.flush()).toEqual(['Suspend! [Async]', 'Loading...']);
    expect(ReactNoop.getChildren()).toEqual([]);
    
    
    await advanceTimers(99);
    
    expect(ReactNoop.flush()).toEqual([]);
    expect(ReactNoop.getChildren()).toEqual([]);
    
    await advanceTimers(1);
    
    expect(ReactNoop.flush()).toEqual(['Promise resolved [Async]', 'Async']);
    expect(ReactNoop.getChildren()).toEqual([span('Async')]);
  });
  it('starts working on an update even if its priority falls between two suspended levels', async () => {
    function App(props) {
      return (
        <Suspense fallback={<Text text="Loading..." />} maxDuration={10000}>
          {props.text === 'C' ? (
            <Text text="C" />
          ) : (
            <AsyncText text={props.text} ms={10000} />
          )}
        </Suspense>
      );
    }
    
    ReactNoop.render(<App text="A" />);