[GAMEPLAY] Morgana Black Shield does not put Tahm Devour on CD, and refunds the mana

This is a very reproduceable bug, it happens every time. If Tahm uses Devour on a three-stacked Morgana with Black Shield on, instead of going on cooldown and costing mana, it resets, giving Tahm no Cooldown and refunds the cost of Devour. He can thereby spam W until Black Shield times out, and get his Devour off.

Steps to reproduce:

1. Get into a custom game with Morgana and Tahm on opposing teams.
2. Morgana levels Black Shield, Tahm picks Devour.
3. Meet up somewhere, Tahm builds up three stacks on Morgana with melee.
4. Morgana puts Black Shield on herself.
5. Tahm uses Devour on Morgana.
6. Repeat step 5 ad nauseum.
7. Bug Confirmed.

Can be reproduced at will in build 5.24.15_12_11_17_53 (and earlier, first instance I noticed was around 6th of December 2015)

Side notes: Morgana Black shield does not appear to take Damage from Tahm's Devour, meaning he cannot break the shield with Devour. But seeing as Devour does not go on cooldown nor cost mana, he can literally spam it until black shield goes out, getting the devour anyway.