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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

}
    } else {
      
      
      nextUnitOfWork = failedUnitOfWork;
    }
  };
  rethrowOriginalError = () => {
    throw originalReplayError;
  };
}
function resetStack() {
  if (nextUnitOfWork !== null) {
    let interruptedWork = nextUnitOfWork.return;
    while (interruptedWork !== null) {
      unwindInterruptedWork(interruptedWork);
      interruptedWork = interruptedWork.return;
    }
  }
  if (__DEV__) {
    ReactStrictModeWarnings.discardPendingWarnings();
    checkThatStackIsEmpty();
  }
  nextRoot = null;
  nextRenderExpirationTime = NoWork;
  nextLatestAbsoluteTimeoutMs = -1;
  nextRenderDidError = false;
  nextUnitOfWork = null;
}
function commitAllHostEffects() {