[GAMEPLAY] Zilean's passive doesn't work on Yuumi if she's attached

Zilean is unable to use his passive to level up an allied Yuumi if she's attached to another ally (I'm not sure if it's also the case when Yuumi is attached to Zilean). You can still see the circle around Yuumi indicating you can level her up, but you can't actually do it because you can't click on her.