I didn't find Raze did much damage, the only difficulty was hitting him hard enough between heals. But I had very high magic resistance, what's your magic resistance? It might be worth beefing it up if you can - potions, charms, equipment etc.
I'd doubt it was a bug (as at least he's doing finite damage), but you'll need to give some info about your build. It does seem too high though: I only had about 700 health when fighting Raze, and I'm not sure I could have done it if I was being hit that hard.
Welcome to the English part of the forums! I wish I could speak French as well as you speak English - or at all for that matter