<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
-->

**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

fn: (A, B, C0, D) => R,
  a: A,
  b: B,
  c: C0,
  d: D,
): R {
  const previousExpirationContext = expirationContext;
  expirationContext = Sync;
  try {
    return fn(a, b, c, d);
  } finally {
    expirationContext = previousExpirationContext;
  }
}
// TODO: Everything below this is written as if it has been lifted to the
// 
// Linked-list of roots
let firstScheduledRoot: FiberRoot | null = null;
let lastScheduledRoot: FiberRoot | null = null;
let callbackExpirationTime: ExpirationTime = NoWork;
let callbackID: *;
let isRendering: boolean = false;
let nextFlushedRoot: FiberRoot | null = null;
let nextFlushedExpirationTime: ExpirationTime = NoWork;