Bug or WAD: Veigar's Event Horizon

I've been playing Veigar for a while now, and it seems some units are able to move through the stun and others cannot, or so it appears as such. A recent example involves Yasuo. He was clearly able to jump through the stun unaffected whereas others like Volibear--while he is charging--cannot. The Yasuo player told me the trick is that he needed to jump through a minion on the corner of the stun in order to bypass the stun's effect. I cannot speak for the validity of this statement other than what I observed: it definitely appeared Yasuo was doing exactly as the player described. Yasuo is not the only unit either. This appears to happen quite often with "jumpers" and although it may be do to some of them getting through before the 0.5 second delay, this is not for every case. If this is WAD, would the developers be so kind as to list the units and which ones--and what ability allows them to do so--are able to bypass the stun? Thanks again -Jimmy