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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

}, ms),
    );
    return resourcePromise;
  }, ([text, ms]) => text);
  AsyncText = ({ms, text}) => {
    try {
      TextResource.read([text, ms]);
      yieldForRenderer(`AsyncText [${text}]`);
      return text;
    } catch (promise) {
      if (typeof promise.then === 'function') {
        yieldForRenderer(`Suspend [${text}]`);
      } else {
        yieldForRenderer(`Error [${text}]`);
      }
      throw promise;
    }
  };
  Text = ({text}) => {
    yieldForRenderer(`Text [${text}]`);
    return text;
  };
}
const mockDevToolsForTest = () => {
  jest.mock('react-reconciler/src/ReactFiberDevToolsHook', () => ({
    injectInternals: () => {},
    onCommitRoot: () => {},
    onCommitUnmount: () => {},
    isDevToolsPresent: true,
  }));