A novela oficial do filme indica que ele pode ter intencionalmente mantido para se dar um lembrete constante para não se tornar complacente.
She reached up to the burn-scar high on his cheek. “You were hurt...”
“Nothing serious,” he said with half a smile. “Just an unfriendly reminder to keep up with my lightsaber practice.”
Star Wars Episode III: Revenge of the Sith - Official Novelisation