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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

} else {
            ReactNoop.yield(`Promise resolved [${text}]`);
            resolve(text);
          }
        }, ms),
      );
    }, ([text, ms]) => text);
    textResourceShouldFail = false;
  });
  
  
  
  
  
  
  function span(prop) {
    return {type: 'span', children: [], prop, hidden: false};
  }
  function advanceTimers(ms) {
    
    
    if (typeof ms !== 'number') {
      throw new Error('Must specify ms');
    }
    jest.advanceTimersByTime(ms);
    
    
    return Promise.resolve().then(() => {});
  }
  function Text(props) {