WSA and WP8 differ, you can see the difference in EventDelegate.Cache. WP8 should be executing line 358, and it's either:
mMethod = type.GetMethod(mMethodName, BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
or
mMethod = type.GetMethod(mMethodName);
...depending on when you grabbed the update. If it's not one, try the other, let me know which one works.