Why does regen go down whenever Spectre's Cowl is upgraded?

In the latest patch (5.3), Riot buffed so that it now has 150% base health regeneration, from 100% in previous patches.

But we all know that when we buy it we plan on upgrading it into either or . The problem is that those items only have the 100% base health regeneration, instead of the 150% offers.

"Just giving fighters and tanks a little help when dealing with mages in lane."

The thing is, whenever or is completed, your health regen will effectively go down (although I do not know if the 20% increased regen of counteracts this). Was this intentional? Or was this intended for the bonus effects each item gives?

Please answer, Riot, and thank you!