title: ITargetLocator's ParentFrame() throws "Invalid Command Method" exception
body: <p>I'm using PhantomJS and selenium WebDriver, all recently downloaded using NuGet so should be the latest version. All I have is a page that contains an iframe element and this code (after navigating to the page):</p>
  
  <pre><code>driver.SwitchTo().Frame(driver.FindElement(By.TagName("iframe")));
  driver.SwitchTo().ParentFrame();
  </code></pre>
  
  <p>The last line throws a "Invalid Command Method" exception. Am I doing something wrong or is this a bug? </p>