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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

// 
        expirationTime = computeInteractiveExpiration(currentTime);
      } else {
        // 
        expirationTime = computeAsyncExpiration(currentTime);
      }
      // 
      // 
      if (nextRoot !== null && expirationTime === nextRenderExpirationTime) {
        expirationTime -= 1;
      }
    } else {
      // 
      expirationTime = Sync;
    }
  }
  if (isBatchingInteractiveUpdates) {
    // 
    // 
    // 
    if (
      lowestPriorityPendingInteractiveExpirationTime === NoWork ||
      expirationTime < lowestPriorityPendingInteractiveExpirationTime
    ) {
      lowestPriorityPendingInteractiveExpirationTime = expirationTime;
    }
  }
  return expirationTime;
}
function renderDidSuspend(