New Post: Navigation for Win Phone 8

I'm running into problems with navigation on WinPhone 8. When I do the following:

_navigation.UriFor<MyViewModel>().WithParam(vm => vm.Id, 1).Navigate();

An ArgumentException is thrown in Microsoft.Phone.ni.dll with the message "Navigation is only supported to relative URIs that are fragments, or begin with '/', or which contain ';component/'.Parameter name: uri"

It seems to me that the URL that is generated by UriFor<>() should begin with a '/', but it does not. Is this a bug in Caliburn Micro or am I doing something wrong?