jsf - Why do only shared project facelets libraries get registered automatically?

Question

Why do my shared facelets libraries not need to be registered via a context parameter in web.xml or web-fragment.xml?

I have a project exclusive tag library which must be added via javax.faces.FACELETS_LIBRARIES else it is not being recognized and components are not rendered.

But all tag libraries in my shared project are added without any declarations.

This is unconsistent behavior.

Glassfish 3.1.2 Mojarra 2.1.21