Sion Ult + Azir Ult Bug

When Sion is in the middle of his Unstoppable Onslaught (R), if he comes into contact with a friendly (teammate) Azir's Emperor's Divide (R), he will stop as if he has collided with terrain. Seeing as how Emperor's Divide is not considered terrain for teammates, as they can move through it, shouldn't Sion's ult also move through it undeterred? If this is the interaction you (Riot) have intended, then please let me know! But i think this is a bug that has somehow slipped through the cracks, and as a Sion main i would like to see it fixed!

Thank you, FightingChicken