It sais on mmo-champion:

Shaman

2.3.2 PTR Notes update

Earth Shield (Restoration) mana cost reduced, now it has a 30 second cooldown.

Is this real?

First you made resto for a huntard nothing more than a toy to play with and now we get a 30 CD?

---

Q u o t e:
because of the bug where you can't
renew the earth shield because "A more powerful spell is already active" (it's not more powerful, pop your
healing trinkets and you still can't override it). The only way out of that is to buff yourself with Earth Shield so
it's removed from your target and then rebuff your target with Earth Shield.

---

I thought it may interest you to know that a few issues with the 'more powerful spell' mechanic have been identified and are due to be fixed in 2.3.2
These fixes should solve the problem described above.