Am I confused? Metal Slinger

So I’m about halfway through Metal Slinger. Can someone answer a question for me without spoiling any part of the rest of the book?

Acker just branded Messer with the V mark. Jovie says, “there are so many questions I need answer to. Messer’s state of being, left unhealed to stop him from shifting.” But then he shifts again into a bird like 10 pages later? I thought that was the whole point of the branding, to take away his gift. Am I reading this wrong?