When I right-click a method and select "Go to implementation", I often present two implementations; one in my source code and one as a link ...

In this example, the EmailService is in another project, which is loaded into the current Visual Studio solution and referred to as a project link.
Selecting the reference unit does not seem to do anything, while choosing the source code leads me to implement the method (as expected).
This happened on several different development machines in different projects.
What causes this, and is it possible to fix the problem in order to proceed with the implementation directly to the implementation of the source code?
This happens in Visual Studio 2012 with ReSharper 7.1 installed.
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