title: WP8: Any idea why OnInvoke not called in derived ScheduledTaskAgent
body: <p>Using Lumia 920, it looks like my OnInvoke is never called even in Debug mode. The Constructor of ScheduledAgent that is inherited from ScheduledTaskAgent is called. Which means that the setup in WMAppManifest.xml is correct. </p>
  
  <pre><code>&lt;Tasks&gt;
    &lt;DefaultTask Name="_default" NavigationPage="MainPage.xaml" /&gt;
    &lt;ExtendedTask Name="BackgroundTask"&gt;
      &lt;BackgroundServiceAgent Specifier="ScheduledTaskAgent" Name="PeriodicAgent" Source="ScheduledPlaybackAgent" Type="ScheduledPlaybackAgent.ScheduledAgent" /&gt;
    &lt;/ExtendedTask&gt;
  &lt;/Tasks&gt;
  </code></pre>
  
  <p>Then I pretty much copied from sample code:</p>
  
  <pre><code>    private void StartPeriodicAgent()
      {
          // Obtain a reference to the period task, if one exists
          periodicTask = ScheduledActionService.Find(periodicTaskName) as PeriodicTask;
  
          if (periodicTask != null)
          {
              RemoveAgent(periodicTaskName);
          }
  
          periodicTask = new PeriodicTask(periodicTaskName);
  
          periodicTask.Description = "This demonstrates a periodic task.";
  
          try
          {
              ScheduledActionService.Add(periodicTask);
          }
          catch (InvalidOperationException exception)
          {
          }
          catch (SchedulerServiceException)
          {
          }
      }
  </code></pre>
  
  <p>I purposely switch to Home screen after foreground app is started and waited as much as I can. Still no output or breakpoint from my ScheduledAgent::OnInvoke</p>
  
  <p>Thanks!</p>