<!--
  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

Placement,
  ContentReset,
  DidCapture,
  Update,
  Ref,
} from 'shared/ReactSideEffectTags';
import ReactSharedInternals from 'shared/ReactSharedInternals';
import {
  debugRenderPhaseSideEffects,
  debugRenderPhaseSideEffectsForStrictMode,
  enableProfilerTimer,
} from 'shared/ReactFeatureFlags';
import invariant from 'shared/invariant';
import shallowEqual from 'shared/shallowEqual';
import getComponentName from 'shared/getComponentName';
import ReactStrictModeWarnings from './ReactStrictModeWarnings';
import warning from 'shared/warning';
import warningWithoutStack from 'shared/warningWithoutStack';
import * as ReactCurrentFiber from './ReactCurrentFiber';
import {startWorkTimer, cancelWorkTimer} from './ReactDebugFiberPerf';
import {
  mountChildFibers,
  reconcileChildFibers,
  cloneChildFibers,
} from './ReactChildFiber';
import {processUpdateQueue} from './ReactUpdateQueue';
import {NoWork, Never} from './ReactFiberExpirationTime';
import {ConcurrentMode, StrictMode} from './ReactTypeOfMode';
import {
  shouldSetTextContent,