Drop-in Chooser on Windows Phone 8.1

Okay, we actually managed to reproduce the behavior you're seeing. The alert was indeed the problem, though I don't understand how. (The alert on the background page seems to have blocked the Chooser page from actually closing?)

In any case, this works for us too on Windows Phone 8.1 Update 1. We're trying to track down a Windows Phone 8.1 without any updates to verify that it works on all versions of Windows Phone 8.1. If it does, we'll change the logic in the library to allow use on Windows Phone 8.1.