Ezreal Q Duskblade doesn't refresh if constantly out of vision

Apparently it seems that when an Ezreal hits an enemy with his Q (and bought Duskblade), that he needs to be seen by an enemy champion to get the Duskblade-buff again. So if you're constantly out of vision of enemy Champions and poking with your Q, you can proc the Duskblade just one time unless an enemy Champion spots you. I don't think this is intended.