For some reason, there are a few veileds that, as adult males, seem to shed a thick section of the front of their casques off. I don't know too much about it, but I see it on here from time to time.
My Tommy was one that lost a piece of the front edge of his casque in one lump. The only reason I could find was that he wasn't misted properly before I got him and I presumed that layers and layers of shed had got hardened on there. He would shed right up to the thickened skin but it never came off until one day he knocked it off himself. I could bathe it to soften it to some extent but it was so thick I was unable to remove it.