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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 pendingInteractionMap = root.pendingInteractionMap;
      pendingInteractionMap.forEach(
        (scheduledInteractions, scheduledExpirationTime) => {
          // 
          // 
          // 
          if (scheduledExpirationTime > earliestRemainingTimeAfterCommit) {
            pendingInteractionMap.delete(scheduledExpirationTime);
            scheduledInteractions.forEach(interaction => {
              interaction.__count--;
              if (subscriber !== null && interaction.__count === 0) {
                try {
                  subscriber.onInteractionScheduledWorkCompleted(interaction);
                } catch (error) {
                  
                  
                  if (!hasUnhandledError) {
                    hasUnhandledError = true;
                    unhandledError = error;
                  }
                }
              }
            });
          }
        },
      );
    }
  }
}
function resetChildExpirationTime(