Kassadin Q Procs Sheen Even if it Doesn't Go On Cooldown [GAMEPLAY]

While playing Kassadin, I noticed that when I would use my Q [Null Sphere] on a minion that died immediately after, my Q would have it's cooldown reset because it wasn't able to fully cast, but I would receive a Sheen [SPELLBLADE] proc. My Q would not be on cooldown and I could cast it again, giving me the ability to use the [SPELLBLADE] passive damage and use [Null Sphere] right afterwards to receiver another proc. Although this isn't game-breaking, I don't think it's working as intended.

How to duplicate this bug:

1. Use Kassadin's Q [Null Sphere] on a minion or monster that is about to die from another damage source while you have Sheen or an item that has the [SPELLBLADE] passive equipped. If you do it correctly your Q cooldown will have reset as the cast did not complete.
2. You will now have a [SPELLBLADE] passive effect on you even though you did not fully cast an ability. Attack an enemy unit to proc this effect, and you will be able to immediately cast [Null Sphere] as it never went on cooldown.

Like I said, this isn't a game-breaking bug, but it can result in extra damage that wasn't intended to be possible.