Stealth Detecting Mist does not give assist

I was playing a game of Twisted Treeline & the enemy team had a Twitch.

I had purchased

Me and my partner were chasing a twitch when he went invisible. I used the Active Ability to reveal him, allowing my partner to pick up the kill.

I got no assist from doing this even though I was the solid reason the twitch died.

Also another thing. How come the Udyr Taunt/Joke bug hasn't been fixed yet? It has been around for a long time.