title: Observable.merge behaves differently in an epic
body: <p>In a React/Redux application, I use Redux Observable and I want an epic to output two distinct actions.</p>
  
  <p>First, I tried this:</p>
  
  <pre><code>const epic1 = action$ =&gt;
    action$
      .ofType("A")
      .mapTo({ type: "B" })
      .merge(Observable.of({ type: "C" }));
  </code></pre>
  
  <p>As it didn't work, I had to switch to:</p>
  
  <pre><code>const epic2 = action$ =&gt;
    action$
      .ofType("D")
      .mergeMap(value =&gt;
        Observable.merge(
          Observable.of({ type: "E" }),
          Observable.of({ type: "F" })
        )
      );
  </code></pre>
  
  <p>See this CodeSandbox <a href="https://codesandbox.io/s/l52ym6n8vz" rel="nofollow noreferrer">example</a>.</p>
  
  <p>The thing is, I'm not sure to understand why the first try didn't work because in the example below, it works well outside an epic:</p>
  
  <pre><code>var observable = Observable.of({type: "A"})
    .mapTo({type: "B"})
    .merge(Observable.of({ type: "C" }));
  
  observable.subscribe(value =&gt; {
    this.setState(prevState =&gt; ({
      values: [...prevState.values, value]
    }));
  });
  </code></pre>
  
  <p>Any idea why it behaves differently in the epic?</p>