Since the original post was on the beta forums and those have since been deleted/archived we have to use wowhead for the original blizzard post.
“Players won’t be able to win multiples of the same item - say that 2 sets of Shoulders drop. While you can roll Need on both of them, winning one will ‘remove’ your roll from the other.”
So i’ll say it again if this truly is happening then it is a bug that should be reported.