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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

'React. Please file an issue.',
      );
      workInProgress.effectTag = (effectTag & ~ShouldCapture) | DidCapture;
      return workInProgress;
    }
    case HostComponent: {
      popHostContext(workInProgress);
      return null;
    }
    case SuspenseComponent: {
      const effectTag = workInProgress.effectTag;
      if (effectTag & ShouldCapture) {
        workInProgress.effectTag = (effectTag & ~ShouldCapture) | DidCapture;
        
        
        const current = workInProgress.alternate;
        const currentState: SuspenseState | null =
          current !== null ? current.memoizedState : null;
        let nextState: SuspenseState | null = workInProgress.memoizedState;
        if (nextState === null) {
          
          nextState = {
            alreadyCaptured: true,
            didTimeout: false,
            timedOutAt: NoWork,
          };
        } else if (currentState === nextState) {
          
          
          nextState = {