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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

popLegacyContext(failedUnitOfWork);
        }
        break;
      }
      case HostPortal:
        popHostContainer(failedUnitOfWork);
        break;
      case ContextProvider:
        popProvider(failedUnitOfWork);
        break;
    }
    
    isReplayingFailedUnitOfWork = true;
    originalReplayError = thrownValue;
    invokeGuardedCallback(null, workLoop, null, isYieldy);
    isReplayingFailedUnitOfWork = false;
    originalReplayError = null;
    if (hasCaughtError()) {
      const replayError = clearCaughtError();
      if (replayError != null && thrownValue != null) {
        try {
          
          
          if (replayError._suppressLogging) {
            
            (thrownValue: any)._suppressLogging = true;
          }
        } catch (inner) {
          
        }