<!--
  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

state = {
          name: 'foo',
        };
        componentDidMount() {
          this.setState({
            name: 'bar',
          });
        }
        render() {
          return <Text text="Loading..." />;
        }
      }
      class Demo extends React.Component {
        render() {
          return (
            <Suspense fallback={<Fallback />}>
              <AsyncText text="Hi" ms={100} />
            </Suspense>
          );
        }
      }
      ReactNoop.renderLegacySyncRoot(<Demo />);
      expect(ReactNoop.getChildren()).toEqual([span('Loading...')]);
      await advanceTimers(100);
      expect(ReactNoop.getChildren()).toEqual([span('Hi')]);
    });
  });
  it('does not call lifecycles of a suspended component', async () => {
    class TextWithLifecycle extends React.Component {