Vayne able to WALK through J4 Ult

A few games ago I was playing J4 jungle, and every time I ulted this vayne she abused a bug, where she would tumble, didn't matter how close she was to the edge of my wall she just tumbled. Then proceeded to WALK out of my ultimate. She literly did this 8/10 times i Ulted her. If she could legitimately tumble out that's fine, but the fact that she could tumble inside it then walk across it then just walk out of it is broken and needs to be fixed.