<!--
  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

shouldDeprioritizeSubtree,
} from './ReactFiberHostConfig';
import {pushHostContext, pushHostContainer} from './ReactFiberHostContext';
import {
  pushProvider,
  propagateContextChange,
  readContext,
  prepareToReadContext,
  calculateChangedBits,
} from './ReactFiberNewContext';
import {prepareToUseHooks, finishHooks, resetHooks} from './ReactFiberHooks';
import {stopProfilerTimerIfRunning} from './ReactProfilerTimer';
import {
  getMaskedContext,
  getUnmaskedContext,
  hasContextChanged as hasLegacyContextChanged,
  pushContextProvider as pushLegacyContextProvider,
  isContextProvider as isLegacyContextProvider,
  pushTopLevelContextObject,
  invalidateContextProvider,
} from './ReactFiberContext';
import {
  enterHydrationState,
  resetHydrationState,
  tryToClaimNextHydratableInstance,
} from './ReactFiberHydrationContext';
import {
  adoptClassInstance,
  applyDerivedStateFromProps,
  constructClassInstance,