Issue with Wooglet's Witchcap in TT

Hi, so i play a decent amount of twisted treeline and last night I was playing and I bought Wooglet's Witchcap. I looked at the passive to see how much extra AP it was giving me and it said 0. at first I thought this was just a bug in the item description. Although, I did a rough calculation after game and calculated that it was in fact not giving me the +25% ability power. there was a chance i did my calculation wrong but I am not sure, can you please take a look at this?

Thank you Water1857