Deathcap Tooltip Bug

I was just playing an ARAM game as Veigar, and bought Deathcap. As you do. But I noticed that when I moused over it it said "increases you AP by 30% (0)". That number stayed at zero the entire game. I went back and tested it, and this bug doesn't happen on Summoner's Rift. On the Howling Abyss the tooltip always says that it is giving you zero bonus AP.

Deathcap is still giving the bonus AP, but the tooltip is busted on the Howling Abyss.