Have you been to Tempest Keep lately? In case you're planning to pay Kael'thas a visit in the near future, be advised that the instance is a bit out of whack. In a thread in the World of Warcraft Forums, players talked about how the weapons in phase 2 of the Kael'thas instance have more HP than usual.

Blizzard poster Daelo dropped by the said thread and here's what he had to say:

We looked into this, and found a new bug. Any of the enchanted weapons that are alive at the point when Prince Kael'thas resurrects his advisors will immediately have their health increased.

We currently cannot hotfix this issue, but we hope to resolve the problem relatively soon.