Do remember this "bug" still exists.

being able to Tumble(Q) through 's ult.

J4's ult description:

Jarvan IV leaps to an enemy champion, dealing physical damage to them and creating a 325-radius circle of impassable terrain around themselves. This circle lasts for 3.5 seconds and also grants sight within 825 range.

"Playing as Vayne tips:

Tumble has many uses, but it cannot pass over walls.

What was promised by Riot Meddler in Patch 4.16:

Jarvan will get stunned against his own wall by Poppy, Vayne and Gnar now, rather than knocked through. I'd expect that to make those match ups noticeably tougher for him, if that hits him too hard we'll look at compensating him in some form. At some point we'll also get Tumble fixed so Vayne can't get out of his ult using it which should even things out a bit too.

But you guys sure were quick on fixing Cait's bug in 2-3 days.