The ST4 library should be completely separate from the ST3 (including the MP2 and Syntronik and Imported and Legacy instruments) library.
ST3, Syntronik and MP2 all reference the same library path. As I mentioned above, this is so that ST3 can also load the Syntronik and MP2 instruments. The path is only stored in one place (on Windows, it is in the Registry) and is accessed by all three products.
Also, have a look at this FAQ:
https://www.ikmultimedia.com/faq/index.php?id=1239