Mage Aatrox ult bug

Hey, I'm afraid I dont have a video showing the bug as I'm not at home rn. I made Aatrox into a mage, and got 6 mages - so he should doublecast ult everytime. According to his tooltip, his ult should cleave the targets in front of him, but as he doublecasted, his first ult went behind him hitting nothing - rendering him completely useless as a mage.