Nunu's Q bug in Ascension?

As I read the description of the Ascension buff on Xerath (The OG Ascension), it states that he may not be consumed or feasted upon, yet I just played a game where a nunu was eating xerath and still applying the true damage, making it near impossible to claim the buff towards the late game when he has a level 5 consume. For additional details, he was in a Zombie Nunu skin (if that somehow causes the bug) and here is the match data http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2151417207/45253884?tab=overview