Darius uses Decimate inside Aqua Prison [GAMEPLAY]

On Summoner's Rift, playing as Nami, I used Aqua Prison on Darius. Just as it was landing, darius cast Decimate, and while he was floating into the air, Decimate was still preparing and cast as if nothing was going on, and proceeded to complete the animation and deal the damage it would have dealt normally, even though Darius was stunned inside the aqua prison and should have been unable to complete the attack.

To recreate this bug:

1. Cast Aqua Prison on Darius.
2. Cast Decimate before the bubble can land.
3. Observe Darius floating in the bubble, yet still winding up and casting Decimate.
4. Move Nami within attack range of Darius.
5. Repeat step 1.
6. Repeat step 2.
7. Observe Darius using Decimate to damage Nami while stunned inside Aqua Prison.

This happened twice in one game I fought against Darius. Both times I watched him float into the air, along with the area of effect sphere, and watched him use Decimate while trapped inside the Aqua Prison. The first time, he actually killed me with it as I was attempting to escape.