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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

// 
          root.finishedWork = finishedWork;
        }
      }
    }
  }
  isRendering = false;
}
function completeRoot(
  root: FiberRoot,
  finishedWork: Fiber,
  expirationTime: ExpirationTime,
): void {
  // 
  const firstBatch = root.firstBatch;
  if (firstBatch !== null && firstBatch._expirationTime >= expirationTime) {
    if (completedBatches === null) {
      completedBatches = [firstBatch];
    } else {
      completedBatches.push(firstBatch);
    }
    if (firstBatch._defer) {
      // 
      // 
      root.finishedWork = finishedWork;
      root.expirationTime = NoWork;
      return;
    }
  }
  //