This has changed in Windows Phone 8.1. From Raw notification overview (Windows Runtime apps)
Receiving a raw notification
There are two avenues through which your app can be receive raw notifications:
- Through notification delivery events while your application is running.
- Through background tasks triggered by the raw notification if your app is enabled to run background tasks.
An app can use both mechanisms to receive raw notifications. If an app implements both the notification delivery event handler and background tasks that are triggered by raw notifications, the notification delivery event will take priority when the app is running.
- If the app is running, the notification delivery event will take priority over the background task and the app will have the first opportunity to process the notification.
- The notification delivery event handler can specify, by setting the event's PushNotificationReceivedEventArgs.Cancel property to true, that the raw notification should not be passed to its background task once the handler exits. If the Cancel property is set to false or is not set (the default value is false), the raw notification will trigger the background task after the notification delivery event handler has done its work.