We've blocked a tv channel/network by going to guide and going to the left where it has the channel logo and number and selected it, which brought up the menu to select Lock and we did. If we go to it now it has the option to unlock, so it's locked. If we are watching the channel below it and press the channel button to go to the one we blocked, it plays the content and doesn't ask for the PIN at all. In Parental Controls and Channel Locks, it shows a channel is locked.
Another issue we've seen is blocking shows in Kid Zone are not blocked. They still show up and we can select and watch them.