Sion E not doing damage to knocked up minions by his Q

I'll have to try to record one of my games but I have noticed this lately from the massive amount of games I've played as Sion. There has been many times where I fully charge my Q on a minion wave, it gets knocked up from my Q I then use my E(Roar of the Slayer) to push a minion into them so that when my W is ready to blow up, it'll clear the wave quite well... Well I noticed that the damage does not happen but the slow still does. If it helps the devs for me to try to make a video for it, I will but I have noticed that anything knocked up by Sion's Q, causes the E to sometimes not deal damage.