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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 errorInfo = value;
        const ctor = workInProgress.type;
        const instance = workInProgress.stateNode;
        if (
          (workInProgress.effectTag & DidCapture) === NoEffect &&
          (typeof ctor.getDerivedStateFromError === 'function' ||
            (instance !== null &&
              typeof instance.componentDidCatch === 'function' &&
              !isAlreadyFailedLegacyErrorBoundary(instance)))
        ) {
          workInProgress.effectTag |= ShouldCapture;
          workInProgress.expirationTime = renderExpirationTime;
          
          const update = createClassErrorUpdate(
            workInProgress,
            errorInfo,
            renderExpirationTime,
          );
          enqueueCapturedUpdate(workInProgress, update);
          return;
        }
        break;
      default:
        break;
    }
    workInProgress = workInProgress.return;
  } while (workInProgress !== null);
}
function unwindWork(