Isn't the CC info sent from the network? Wouldn't the problem be on their end? If CC works at least once on one show/network, then the CC system should be considered "functional", and therefore is a show-by-show issue.
We use CC for some shows, like "The Office" since there are often some comments under the breath of the actors that are quite funny, but with the volume at a respectable level, they are sometime impossible to hear. We don't want to wake the kids, so CC works there. But on the CSI we just watched tonight from two nights ago, the CC didn't work. Changed to something on NatGeo and it worked just fine. So for me, the problem goes from show to show and from network to network.
EDIT: I have 2 HR20-700's, both with HDMI hook-ups, and the "issue" is identical on both.