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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

reconcileChildren(null, workInProgress, value, renderExpirationTime);
    return workInProgress.child;
  }
}
function updateSuspenseComponent(
  current,
  workInProgress,
  renderExpirationTime,
) {
  const mode = workInProgress.mode;
  const nextProps = workInProgress.pendingProps;
  
  
  let nextState: SuspenseState | null = workInProgress.memoizedState;
  if (nextState === null) {
    
  } else {
    if (!nextState.alreadyCaptured) {
      
      
      nextState = null;
    } else {
      
      
      if (current !== null && nextState === current.memoizedState) {
        
        nextState = {
          alreadyCaptured: true,
          didTimeout: true,
          timedOutAt: nextState.timedOutAt,