I Just finished a match where the was a bug that happened. There were only 3 players left. I was on Jandice Barov, and the opponent I was facing was Yogg-saron.
I was playing murlocs so I had a fair amount of reborn on the board. My opponent had 7 health left, after the battle ended, I won the round and the last minion I had on my board was Bubble Gunner, which had reborn so it had one health left.
Being on tier 6 + 1 from minion tier, It should have knocked him out of the game as it was a total of 7 dmg. However, for some reason when my hero attacked him it hit for 0 damage. It also showed zero dmg in the left pane bar.
He did not discover any buddies that would have given him immunity for the round, so no secrets, his hero power did not change, he should have died when I attacked him. His warband was Beast Beatles.
I have never seen this happen before. I was pretty shocked to see my hero attack his hero and hit for 0 on tier 6 after destroying their entire warband.