For anyone reading this thread thinking that this ruling is the latest (like I did):
It is not.
Donald changed his ruling in 2011. See this post:
Quote from Donald:
You only keep TR and KC in play if they directly played a duration card. If you KC a KC a duration card, the first KC is discarded, the second stays in play.
This is just the most direct interpretation of the rulebook. Briefly I said both stayed out, but the way of specifying that is convoluted and anyway did not match the rulebook.