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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

: updateExpirationTimeAfterCommit;
  if (earliestRemainingTimeAfterCommit === NoWork) {
    
    
    legacyErrorBoundariesThatAlreadyFailed = null;
  }
  onCommit(root, earliestRemainingTimeAfterCommit);
  if (enableSchedulerTracing) {
    __interactionsRef.current = prevInteractions;
    let subscriber;
    try {
      subscriber = __subscriberRef.current;
      if (subscriber !== null && root.memoizedInteractions.size > 0) {
        const threadID = computeThreadID(
          committedExpirationTime,
          root.interactionThreadID,
        );
        subscriber.onWorkStopped(root.memoizedInteractions, threadID);
      }
    } catch (error) {
      
      
      if (!hasUnhandledError) {
        hasUnhandledError = true;
        unhandledError = error;
      }
    } finally {