Originally Posted by VeWt
People are looking at the wrong side of the ability interaction. This is caused by the delay between omni's forswing for repel and the ability taking effect, which while infinitesimally small, exists. Evidently the delay is long enough for the stun on HM to be applied, but not for the damage. I have also witnessed and tested this with other stuns in the past, and while very hard to reproduce, it does exist.
You did notice that first the damage is dealt and then the stun is cast? This makes your argument invalid.
I'd have accepted an argument if the stun was cast first and then the damage would be applied, in which case the stun might indeed take (very) few gameticks to actually hit the target, resulting in stun after damage, if that had been the observation. However, this wasn't the case (we are talking about stun without damage).
It's probably technically possible to take the damage but not get stunned. But i'm not sure how wc3 handles those stuns with 9999 missile speed cast from 0 distance in relation to other events.