<!--
  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

// Because this fiber did not complete, don't reset its expiration 
      if (workInProgress.effectTag & DidCapture) {
        // 
        stopFailedWorkTimer(workInProgress);
      } else {
        stopWorkTimer(workInProgress);
      }
      if (__DEV__) {
        ReactCurrentFiber.resetCurrentFiber();
      }
      if (next !== null) {
        stopWorkTimer(workInProgress);
        if (__DEV__ && ReactFiberInstrumentation.debugTool) {
          ReactFiberInstrumentation.debugTool.onCompleteWork(workInProgress);
        }
        if (enableProfilerTimer) {
          // 
          if (next.mode & ProfileMode) {
            let actualDuration = next.actualDuration;
            let child = next.child;
            while (child !== null) {
              actualDuration += child.actualDuration;
              child = child.sibling;
            }
            next.actualDuration = actualDuration;
          }
        }
        // 
        // 
        //