Bug Report - Galio - Gameplay

Hi, So I just played a game where i was sejuani jg against a galio jg. The situation goes like this: From blue side, mid river on top half of map, there are curved bushes a center bush and then the scuttle/baron area farther up the map. Galio begins to fight me over a control ward in river and jax begins to come down to help him. I, as sejuani, hit q to proc cOtC keystone and e to slow on galio before jax is there. I then run down towards jg opening behind 1st mid turret. Galio and jax cluster and i see the galio jump back for his E(This is the important part, he has done the animation for his justice punch) I ult(r Glacial prison) and I see them both stunned. Then as soon as galio isnt stunned E finishes animation and he knocks me up holding me for the kill. Isn't his E supposed to act simialr to vi q where if Hard CC'd your ability is cancelled and sent to cd?