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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

NoWork,
        );
        primaryChildFragment.effectTag |= Placement;
         
         
        const fallbackChildFragment = (primaryChildFragment.sibling = createWorkInProgress(
          currentFallbackChildFragment,
          nextFallbackChildren,
          currentFallbackChildFragment.expirationTime,
        ));
        fallbackChildFragment.effectTag |= Placement;
        child = primaryChildFragment;
        primaryChildFragment.childExpirationTime = NoWork;
         
         
        next = fallbackChildFragment;
        child.return = next.return = workInProgress;
      } else {
         
         
        const nextPrimaryChildren = nextProps.children;
        const currentPrimaryChild = currentPrimaryChildFragment.child;
        const currentFallbackChild = currentFallbackChildFragment.child;
        const primaryChild = reconcileChildFibers(
          workInProgress,
          currentPrimaryChild,
          nextPrimaryChildren,
          renderExpirationTime,
        );