Upgrade is a downgrade?

I have read this post and still have a question.

My question is:
Ilvl 400 Gorak Tul’s Mantle is rated bettter than the ilvl 415 Gorak Tul’s Mantle in upgrade finder > Titan Residuum? Looks like a bug

Maybe you can unlock an extra ring of traits on the ilvl400 version?