So this just happened to me. I jumped on an enemy black prior who was fighting with one of my guys below, and I have to believe it was a coincidence, he used his overpowered counter just at this moment (RS down + R1). One second I was falling on him, blade first, the next I was getting thrown on the ground over his shoulder like a boring sack of potatoes. He didn't have a speck of HP less than before, neither did I.
Please reassure me that this is a bug and not an intended feature, because the BP counter is just insane as it is. I can live with that move, as unfair as I think it is, but the whole countering a jump attack thing? Especially since I fell like 5m high? It's a bit too much.
If you did not suffer any damage, it is indeed a bug, the sword supposed to hit you by the end of the counter. It beats everything but guardbreaks and it has a draw with traps, but the recovery on fail is very slow. And there is nothing overpowered in that move, if anything is overpowered, it's the shieldbash.