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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 threadID = computeThreadID(
            expirationTime,
            root.interactionThreadID,
          );
          try {
            subscriber.onWorkStarted(interactions, threadID);
          } catch (error) {
            // 
            // 
            
            if (!hasUnhandledError) {
              hasUnhandledError = true;
              unhandledError = error;
            }
          }
        }
      }
    }
  }
  let prevInteractions: Set<Interaction> = (null: any);
  if (enableSchedulerTracing) {
    // 
    // 
    prevInteractions = __interactionsRef.current;
    __interactionsRef.current = root.memoizedInteractions;
  }
  let didFatal = false;
  startWorkLoopTimer(nextUnitOfWork);
  do {
    try {