Darius and Endless buff for the ult

Can someone look at Darius and his ult? I think its bugged cuz he has always 5 stacks, after first kill with ult. I know there is the buff for this but even when this buff ends, he still gets 5 stacks. Sorry for grammar, just please chceck Darius, cuz i think he is bugged after last patch. ( server Eune -> patch -> 5.21.15_10_26_23_49 )