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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

};
describe('Profiler', () => {
  describe('works in profiling and non-profiling bundles', () => {
    [true, false].forEach(enableSchedulerTracing => {
      [true, false].forEach(enableProfilerTimer => {
        describe(`enableSchedulerTracing:${
          enableSchedulerTracing ? 'enabled' : 'disabled'
        } enableProfilerTimer:${
          enableProfilerTimer ? 'enabled' : 'disabled'
        }`, () => {
          beforeEach(() => {
            jest.resetModules();
            loadModules({enableSchedulerTracing, enableProfilerTimer});
          });
          
          
          if (__DEV__ && enableProfilerTimer) {
            it('should warn if required params are missing', () => {
              expect(() => {
                expect(() => {
                  ReactTestRenderer.create(<React.unstable_Profiler />);
                }).toThrow('onRender is not a function');
              }).toWarnDev(
                'Profiler must specify an "id" string and "onRender" function as props',
                {withoutStack: true},
              );
            });
          }
          it('should support an empty Profiler (with no children)', () => {