Gameplay Bug: Rabadon's Deathcap Tooltip

I was playing an ARAM today, and noticed that my teammate was not getting any bonus AP from Rabadon's (at least that's what the tooltip was saying). Not sure if it's just the tooltip that's bugged, going into a custom match to find out more.

Edit: Took screenshots with me, my friend as my enemy and as my teammate. Tooltip seems to be working. Going to try in an acutal ARAM next. Also, sorry for the black and white; photoshop wasn't putting it in color for some reason.