title: startActivity from background service leads to strange task-switching behaviour
body: <p>My app consists mainly of two activities, A and B, and a background service (started by alarms).
  Activity A is the launcher (main) activity. 
  Activity B is started every now and then by the background service, with FLAG_ACTIVITY_NEW_TASK set (this is required for activity starts in bg services).</p>
  
  <p><strong>Desired behaviour</strong>: Whenever the app is left (return to homescreen, backbutton etc.) and the user returns to it, Activity A shall be resumed.</p>
  
  <p><strong>My problem</strong>: Whenever B has been started by the background service, the app will <strong>always</strong> return to B through the activity switcher (home-button long press), no matter if I have closed it via back-button or not. I can then only return to Activity A if I select the home icon of the app (because A is then started as launch activity).</p>
  
  <p>I think this has to do with fact that B is started in a new task by the background service, and the app-switcher tries to return to this new task. But shouldn't the new task end when I close B via back-button, returning to A?</p>
  
  <p>Can someone please explain to me what's the matter here?</p>