What's With The Nerf On Manamune Next Patch?

Tear

>Gold cost :: 750 >>> 850* Mana cost reduction :: 15% >>> 10%* When you gain max mana from Tear of the Goddess's passive, it preserves your percent current mana. E.g. if you had 300 of 600 mana when it awarded you 4 max mana, on live you would have 304 of 604; with this change you would have 302 of 604 instead.*

Manamune

>When you gain max mana from Tear of the Goddess's passive, it preserves your percent current mana.*

I thought Manamune needed a buff for only one person building it, which is Ezreal. Whys the nerf?