Forms >= 1.2.2.6243 breaks Win Phone

I have an existing solution. I tried adding a brand new Win Phone project to it. Works fine without a reference to Forms. As soon as I reference my Core project which references 1.2.2.6243 I get :

    Error   121 Cannot resolve reference assemblies. Please check the reference assemblies. Cannot resolve dependency to assembly 'Xamarin.Forms.Core, Version=1.2.2.0, Culture=neutral, PublicKeyToken=null' because it has not been preloaded. When using the ReflectionOnly APIs, dependent assemblies must be pre-loaded or loaded on demand through the ReflectionOnlyAssemblyResolve event.   C:\WIP\Xamarin_Forms\PhoneApp2\MainPage.xaml    PhoneApp2