No Library Link for generated s-function

I programmed an S-Function and then put it into a library. When I drag and drop the S-Function from the library into a model, the S-Function gets an "Library Link". Now I can go to the library block or disable the link.

Next I took an subsystem and generated an S-Function from the Subsystem. I also put the generated S-Function into the same library. When I drag and drop the generated S-Function from the library into a model, the generated S-Function does NOT get the Library Link. Can someone explain why? Or even better can I somehow get an Library Link on the generated S-Function?