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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

? 22
                    : 19,
                );
                
                expect(updateCall[1]).toBe('update');
                
                expect(updateCall[2]).toBe(22);
                
                expect(updateCall[3]).toBe(22);
                
                expect(updateCall[4]).toBe(
                  __DEV__ && replayFailedUnitOfWorkWithInvokeGuardedCallback
                    ? 22
                    : 19,
                );
                
                
                expect(updateCall[5]).toBe(
                  __DEV__ && replayFailedUnitOfWorkWithInvokeGuardedCallback
                    ? 44
                    : 41,
                );
              });
              it('should accumulate actual time after an error handled by getDerivedStateFromError()', () => {
                const callback = jest.fn();
                const ThrowsError = () => {
                  advanceTimeBy(10);
                  throw Error('expected error');
                };
                class ErrorBoundary extends React.Component {