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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

recordScheduleUpdate();
  if (__DEV__) {
    if (fiber.tag === ClassComponent) {
      const instance = fiber.stateNode;
      warnAboutInvalidUpdates(instance);
    }
  }
  // 
  if (fiber.expirationTime < expirationTime) {
    fiber.expirationTime = expirationTime;
  }
  let alternate = fiber.alternate;
  if (alternate !== null && alternate.expirationTime < expirationTime) {
    alternate.expirationTime = expirationTime;
  }
  // 
  let node = fiber.return;
  let root = null;
  if (node === null && fiber.tag === HostRoot) {
    root = fiber.stateNode;
  } else {
    while (node !== null) {
      alternate = node.alternate;
      if (node.childExpirationTime < expirationTime) {