It looks like a display bug, because I just checked a champ that wasn't duped and went to it and the "Use Item" button was still there, allowing me to use the Gem, but theres no visual representation anywhere that it exist.
Same with the revives, I started a fight, quit out, and went to see if I could revive them and their all there in that screen, there just not visually showing in your main menu inventory tabs.