I like Death Knights.
I don't like heart beats.
Seriously though, I tracked down the problem today. I have a stop-gap measure that will solve all the heartbeat issues with them, but I don't have the real fix yet. So, what I've elected to do is leave them as is (yes, everyone knows they're broken. Yes, it's been many, many years they have been broken. No, another few weeks won't make any big difference) in order to figure out the right full fix and track down whether or not I'll have to hand-edit those that have already been made in order for it to stick.
In short, they'll be fixed as soon as I have the time to learn our save system.