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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

<TextWithLifecycle text="C" />
        </Suspense>
      );
    }
    ReactNoop.renderLegacySyncRoot(<App />, () =>
      ReactNoop.yield('Commit root'),
    );
    expect(ReactNoop.clearYields()).toEqual([
      'A',
      'Suspend! [B]',
      'C',
      'Mount [A]',
      
      
      'Mount [C]',
      'Commit root',
      
      'Loading...',
      'Mount [Loading...]',
    ]);
    expect(ReactNoop.getChildrenAsJSX()).toEqual(
      <React.Fragment>
        <span hidden={true} prop="A" />
        <span hidden={true} prop="C" />
        <span prop="Loading..." />
      </React.Fragment>,
    );
  });
});