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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 ref = workInProgress.ref;
  if (
    (current === null && ref !== null) ||
    (current !== null && current.ref !== ref)
  ) {
    
    workInProgress.effectTag |= Ref;
  }
}
function updateFunctionComponent(
  current,
  workInProgress,
  Component,
  nextProps: any,
  renderExpirationTime,
) {
  const unmaskedContext = getUnmaskedContext(workInProgress, Component, true);
  const context = getMaskedContext(workInProgress, unmaskedContext);
  let nextChildren;
  prepareToReadContext(workInProgress, renderExpirationTime);
  prepareToUseHooks(current, workInProgress, renderExpirationTime);
  if (__DEV__) {