Skirmishers blade

I don't know if I am the only person that has this problem, but whenever I use it I swear if I smite a target lest say Talon then he ults I LOSE vision cause that's hit ult.....but with Skirmishers it stats you gain vision of them for 6 seconds and I know if i smite him then he ults it has not been no 6 seconds, this is just one example of many chaps it happens with Vayne for example is another one. And for one i am curious if this just happens to me or if it's a bug with the item. and for the people who will say it don't grant you vision it states right in the item "You have vision of them" for 6 seconds I have Vision of them.