Not sure where to post this, and also need confirmation.
The bug is simple. There seems to be a small delay in some actions, and if a disabling effect is applied before this action takes full effect, said action is canceled.
I was playing Voodoo Jester, used Acid Cocktail, I saw the animation, the cooldown triggers, my mana was used. But just before it hit, a Tempest used his ult and trapped me. Even though the Acid Cocktail "hit" him, it did not stun him or deal any damage and was effectively cancelled out.
I was playing Pollywog Priest, and used Magical Bindings on a Pyromancer. Again, the cooldown triggered, mana was used and I saw the green lightning like effect. However, just a split second after I used Magical Bindings, the Pyromancer used his AOE stun. I ended up stunned and Magical Bindings cancelled out.
In short, you attack someone, a fraction of a second later, they use a stun or disabling effect on you, which effectively cancels out your first attack, even though it used up mana, triggered a cooldown or displayed an animation effect.
It is kind of annoying, and game breaking if it is a genuine issue. I doubt it was lag because in both games I had a reported ping of less than 80ms (according to the chatroom just before the game starts).
Has anyone else experienced this sort of behaviour? Those are not the only examples I have seen of it, but those are the two most memorable because they weren't in the middle of a chaotic fight.