That was by design - but given the unintended consequences, I changed the behavior in version 0.2.7. You probably have a weapon fragment installed. The fragment adds an element effect to the attack. If you attack an enemy with a fire fragment added to a weapon, the damage becomes fire damage. This is all good when the enemy is weak to fire. It is really bad when the enemy is not only resistant to fire, but fire makes it stronger. I had this great idea the the player would anticipate what elements they needed to attack with an adjust their weapon fragments accordingly. In practice, there is no way anyone is doing that. I changed the weapon fragments to be only element and state resistance fragments. You should not see the "echo's super slash heals the enemies" problem anymore.