Because that is the way I see it? If you elect to use Custom Lineage (which I would never allow, but also not relevant) you are choosing not to be an established race and gain all the benefits that come with that race--including racial feats. So, on the character sheet, list "Custom" to denote you are not something else that is an established race and don't have the traits associated with it. Ex. An half-orc gets Relentless Endurance, a "custom" half-orc clone-thing wouldn't.
You do what you want, since I won't allow it its a non-issue for me anyway.