Pentakill not announced ??

I was playing as Ashe in ARAM game mode. Atthe match i killed all the enemies , i got to quadra and i killed the fifth one but the penta kill wasnt announced even though the little 5 icons of the killing spree-the enemies i killed - were shown at the right of the screen. I read at some forums that the time limit to get a multykilling is 8-10 secs but im sure i did it in the right time and for even if the 5 icons of the dead enemies were shown the penta wasnt announced. Also the voice didnt say that another ally killed an anemy so what the deal? Has that happened to other players as well? was it a bug maybe? i have seen mush of them... I was just curious why did that happen but i m still happy for the pentakill :D [slayer-jinx-catface]