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**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

listeners.forEach(listener => listener.reject(value));
                  } else {
                    ReactTestRenderer.unstable_yield(
                      `Promise resolved [${text}]`,
                    );
                    status = 'resolved';
                    value = text;
                    listeners.forEach(listener => listener.resolve(value));
                  }
                }, ms);
              } else {
                listeners.push({resolve, reject});
              }
              break;
            }
            case 'resolved': {
              resolve(value);
              break;
            }
            case 'rejected': {
              reject(value);
              break;
            }
          }
        },
      };
    }, ([text, ms]) => text);
    textResourceShouldFail = false;
  });
  function Text(props) {