I opened a ticket but looks like they are not aware of this problem. They just keep telling me useless stuff like trying something I already did 100 times, and trying it on a different system, which I did, confirming the fact that the card can't work on 3.0.
But again, they don't look like they know what I'm talking about, so I don't want to spend more money to RMA a card just to get another one with the same issue. I better buy another one from asus, but you know this is not going to make me happy.