my opponent cast a spell using Iroh, Grand Lotus's ability to cast spells from their graveyard, but the client did not give me an opportunity to respond. My opponent's removal spell just resolved as though it had split-second, not even going on the stack, when I had plenty of available mana to use abilities. Confused, I then verified that I had not accidentally auto-passed priority, so I can only conclude this was a bug involving Iroh's ability.