Can't add reference from C# PCL project to F# PCL project as project reference

问题

I wanna add project reference from Xamarin.Forms PCL C# project to F# PCL project, but Visual Studio15 shows alert as "Unable to add a reference to project 'PortableLibrary2'.
Portable Library projects can only reference other Portable Library projects and assemblies." If I use Visual Studio13,it shows "Unable to add a reference to project 'PortableLibrary2'." then 'The method or operation is not implemented.'.

I attached link to sample project on github I created this sample with following steps

1.create F# PCL project named "PortableLibrary2" as profile7
2.create C# Xamarin.Forms blank pcl project named "App1".
3.change profile from App1 project property to profile7

Before I created similar project structure and it could add project reference properly. I can't find difference which makes these different results.

adding reference to compiled PortableLibrary2.dll by Browse works fine properly.

Any idea?

来源：https://stackoverflow.com/questions/34922480/cant-add-reference-from-c-sharp-pcl-project-to-f-pcl-project-as-project-refere