Onslaught of Shadows being stopped mid-charge.
Now, first off I apologize for not having a replay or anything; LoLReplay crashes my client if I ever go into a profile/store tab.
Second, and the reason I made this, is that I just played Hecarim in an ARAM match, and at one point in the middle of a match, the enemy Ahri Charmed me as I was in the middle of my ult that was aimed to go behind her, stopping me from doing so and giving all the effects of being Charmed and such. And yes, it was indeed aimed behind her. Not a case of short-casting the dash indicator.
Now as far as I know, Hecarim's ult works (or is supposed to work) the same way as Malphite and Vi's do, as well as Jarvan's E-Q: where any CC taken during the dash gets applied after the dash is over, but cannot stop the dash itself. But in this case, my dash was cut short and only the ghost riders moved on.
If Hecarim's ult isn't supposed to be the same as the others anymore, and is indeed supposed to be stoppable, then just ignore this. But seeing as I can ult through Emperor's Divide just fine, I'm fairly certain the Charm stopping me isn't working as intended.