What you were expecting to happen, and what actually happened?
Hero is equipped with Crescendo and has 10 magic. It deals 7 true damage to all enemies, and gains 2 magic. After the first use the magic is 12 as it should be. However, Crescendo only deals 8 true damage this round. I used it again after which the magic is correctly stated as 14, but the card now only deals 9 true damage.
What are the steps to make it happen again?
I should probably also mention that this is in the Arena.
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!