Well, sometimes glitches pop up. They aren't pretty, and they are often not repeatable, but it happens. I hit ashe with an ult the other day, and she just casually strolled away from it. No morgana in game, no banshees veil, nothing of that particular effectiveness in play. Sometimes, it just happens.
Jarvan's ultimate can be passed through as Malphite, since his ultimate does go through walls. The only other thought is that Jarvan's ultimate is a very wide area of coverage, and even though you may have had enough distance to travel across one side of it, if the spell's target area of effect was not far enough beyond the other side of his ult, it would just leave you inside it.