This is a placeholder bug.
A customer reported that taking a Web API 2.0 site, and updating the nuget package for web api client succeeded but left the site broken, because the web API 1.0 package was not updated.
Comments: This is unfortunately by design. There is no partial compatibility between MVC4 and MVC5 (or WebAPI1 and WebAPI2), and you will need to update all the packages.
A customer reported that taking a Web API 2.0 site, and updating the nuget package for web api client succeeded but left the site broken, because the web API 1.0 package was not updated.
Comments: This is unfortunately by design. There is no partial compatibility between MVC4 and MVC5 (or WebAPI1 and WebAPI2), and you will need to update all the packages.