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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

componentName: source !== null ? getComponentName(source.type) : null,
    componentStack: stack !== null ? stack : '',
    error: errorInfo.value,
    errorBoundary: null,
    errorBoundaryName: null,
    errorBoundaryFound: false,
    willRetry: false,
  };
  if (boundary !== null && boundary.tag === ClassComponent) {
    capturedError.errorBoundary = boundary.stateNode;
    capturedError.errorBoundaryName = getComponentName(boundary.type);
    capturedError.errorBoundaryFound = true;
    capturedError.willRetry = true;
  }
  try {
    logCapturedError(capturedError);
  } catch (e) {
    
    
    
    
    setTimeout(() => {
      throw e;
    });
  }
}
const callComponentWillUnmountWithTimer = function(current, instance) {
  startPhaseTimer(current, 'componentWillUnmount');
  instance.props = current.memoizedProps;
  instance.state = current.memoizedState;