I already posted this in the "bugs" thread, but I think it's worth a separate thread (since it's not actually a bug I guess, but more a feedback). Sorry for kind of a double-post.
The thing is that I had problems with accidentally exiting the app.
I think it's not absolutely clear that tapping the (blue/orange "blinking") notification-icon in the upper right corner doesn't actually perform a navigation (at least if you're on the first page), but is rather a shortcut to the second pivot-item on the first page (the "recent" tab).
But also if you're on any page (a conversation for example), than tap the (orange-blinking) notifications-icon, it brings you to the first page's "recent"-section (pivot-item).
If you now want to "navigate back" to the previous page/conversation, you would hit the back-button (like you're used to). But instead of going back to the conversation/contacts-list, this exits the application (because you're on the first page in the back-stack) ...
I think that's not good practice and confuses the user who is not used to this behavior. You might reconsider your navigation-model
thanks so far,