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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

const text = props.text;
        useLayoutEffect(
          () => {
            ReactTestRenderer.unstable_yield('Did commit: ' + text);
          },
          [text],
        );
        try {
          TextResource.read([props.text, props.ms]);
          ReactTestRenderer.unstable_yield(text);
          return text;
        } catch (promise) {
          if (typeof promise.then === 'function') {
            ReactTestRenderer.unstable_yield(`Suspend! [${text}]`);
          } else {
            ReactTestRenderer.unstable_yield(`Error! [${text}]`);
          }
          throw promise;
        }
      }
      function App({text}) {