Maybe a bug?

So , i was playing ARAM ( http://matchhistory.eune.leagueoflegends.com/en/#match-details/EUN1/1343844878/37127291 ) their team had cc champs and i bought qss , I pressed it and it didn't work at all ... it was't once , it was at least 4-5 time in this game , I don't know if it's a bug or not . Can someone explain this to me ,please? :) Thank you!