[GAMEPLAY] Jarvan piggyback on Sion's Ultimate

I was playing Sion. Fighting Jarvan. I was losing. I used Sion's ult to charge toward the safety of one of my team's towers. I know jarvan ult temporarily makes terrain and that crashing into terrain stops Sion's ult; That's NOT what happened . I successfully went hurtling across the map, even past my tower, for the full duration of Sion's ult. I thought I was safe. Immediately after Sion's ult ended Jarvan appeared right on top of me when he wasn't there before and his catalysm ring apeared around me. This was AFTER I charged halfway across the map away from Jarvan. Jarvan was nowhere near me. Note, there was no ward J4 teleported to or something to head me off; I would have seen the ward and him teleport in. He just apeared right on top of me, ulted, and boom! I'm dead. WTF? I'm not sure exactly what happened, but maybe if jarvan ults sion WHILE sion is charging jarvan's ult is delayed until Sion's charge ends and then it goes active?