Maybe I don't have the "last" Poison move, but I have never seen an enemy not be able to heal after being hurt, either by poison or more conventional attacks. The reason for this response is you failed to mention what the Poison attack is called and I can't research it.
I know right. I'm saddened at the fact they took the time to fix musketeers two powers and buccaneers power and install all those extra update yet they didn't fix our power. Maybe next update?