rift being on ward slot

why is rift on ward slot ? -_-
it happend to me many times when im in a fight and i have rift and enemy dashes into bush i quickly press my ward hot key to ward the bush and ding dong :) , i mean it can be in an inventory slot , i m so used to pressing bottons that some times i dont even think about what im pushind my hands just do it ... and well ... warding is pretty important ya know ? :(