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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

);
        },
      );
      expect(onInteractionTraced).toHaveBeenCalledTimes(1);
      expect(onInteractionTraced).toHaveBeenLastNotifiedOfInteraction(
        interactionCreation,
      );
      expect(onInteractionScheduledWorkCompleted).not.toHaveBeenCalled();
      
      
      expect(getWorkForReactThreads(onWorkStarted)).toHaveLength(0);
      expect(getWorkForReactThreads(onWorkStopped)).toHaveLength(0);
      
      
      
      expect(onWorkScheduled).toHaveBeenCalled();
      expect(onWorkScheduled.mock.calls[0][0]).toMatchInteractions([
        interactionCreation,
      ]);
      expect(onWorkScheduled.mock.calls[0][1] > 0).toBe(true);
      
      renderer.unstable_flushAll(['first', 'last']);
      expect(onRender).toHaveBeenCalledTimes(1);
      let call = onRender.mock.calls[0];
      expect(call[0]).toEqual('test-profiler');
      expect(call[5]).toEqual(mockNow());
      if (ReactFeatureFlags.enableSchedulerTracing) {
        expect(call[6]).toMatchInteractions([interactionCreation]);
      }
      expect(onInteractionTraced).toHaveBeenCalledTimes(1);