[Gameplay] Elixir of Sorcery persisting after duration? (Howling Abyss)

Before I actually go on about the issue, I just want to say that I can't confirm this on SR or TT. I've only noticed it on HA.

So the game is going along just fine, no issues, until I decide to buy the Elixir of Sorcery. It did its job when I bought it; increasing my damage to towers and doing additional true damage to champions. But.. when the duration ran out, I continued to do increased damage to towers. My attack was only at around 100, maybe 101, but I was hitting for 236 on their second tower, inhibitor, nexus turrets, and the nexus. As a Lux. And I built no attack damage items, as you can see in the image. (I edited it into the one picture)

I could be wrong, and please tell me if I am. But I was chunking towers down and it didn't seem right.