Geocoder does not work from background thread in Windows Phone.

If I run:

var coder = new Geocoder();
var partnerPosition = (await coder.GetPositionsForAddressAsync(partner.Address)).FirstOrDefault();

I get a cross-thread execution exception. If I try to wrap the code in Device.BeginInvokeOnMainThread, it executes but returns no results. I can successfully call the above code in the constructor of a Page, and it executes correctly.