So…yeah, that 3/1 to 3/2 buff does literally nothing. It is the most sad and pathetic “buff” I have ever seen. Even the old +1 to charge minions meme has nothing on this.
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Boy they sure shook up the meta didn’t they? 
AFAIK, when your minion actually loses taunt or reborn, it still triggers.
This can happen when it is attacked with Sin’dorei Straight Shot