I had the same problem. Opponent cast coerced to kill on my Agrus Kos, Spirit Of Justice. I cast doppelgang targeting the coerced to kill and one of my riftburst hellion. It's almost like it wanted you to submit 2 but would only allow you to submit one but because I hadn't submitted to. I had to wait until the game timed out.
I had the same problem. Opponent cast coerced to kill on my Agrus Kos, Spirit Of Justice. I cast doppelgang targeting the coerced to kill and one of my riftburst hellion. It's almost like it wanted you to submit 2 but would only allow you to submit one but because I hadn't submitted to. I had to wait until the game timed out.