Death Knights have been... very bugged since I started playing Darke. They still make you lose heartbeat more or less every time you try to fight them. As things are, you could (ab)use them to make your castle quite, quite unlootable. ...and that's not to mention the possible abuses in playerkilling.
Several arches have claimed during the years to have un-bugged them, but the same problem still remains. I think it's a wonder that they arent abused more than they are. Why not just remove them until a new Death Knight, thoroughly tested and certain not to make people lose heartbeat is coded?
Furthermore... CPR does not work almost ever if you lose heartbeat. Well, I have never seen it work on Darke, the few times I have lost heartbeat...