One of the ways to build a universal app is to use the partial keyword to allow you to split out functionality that must be different between platforms.
We tried this with our error reporting code, loosely based on LittleWatson.
There is good documentation here http://msdn.microsoft.com/en-us/library/wa80x488(v=vs.90).aspx on partial classes, but despite what it said we just couldn’t get it to work correctly. So we concocted more and more bizarre ways to use partial, so that the program would compile, including partial methods (which unless implemented the compiler optimizes out).
In the end, it turned out to be nothing related to partial at all, that was preventing our methods from being called. What had actually gone wrong was this: We had inadvertently put half of the partial class in a different namespace, thereby making it invisible. It’s no wonder we couldn’t find member fields in our main implementation.