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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.getChildren()).toEqual([span('(empty)')]);
  });
  it('forces an expiration after an update times out', async () => {
    ReactNoop.render(
      <Fragment>
        <Suspense fallback={<Text text="Loading..." />}>
          <AsyncText text="Async" ms={20000} />
        </Suspense>
        <Text text="Sync" />
      </Fragment>,
    );
    expect(ReactNoop.flush()).toEqual([
      
      'Suspend! [Async]',
      
      'Loading...',
      
      'Sync',
    ]);
    
    expect(ReactNoop.getChildren()).toEqual([]);
    
    
    ReactNoop.expire(10000);
    await advanceTimers(10000);
    
    
    expect(ReactNoop.flushExpired()).toEqual([]);