Over the past few weeks I have noticed when viewing TV3 or Nat Geo channel through the Sky digital decoder that the picture is shrunk to about 75% of it's normal size. It is centred on my 29" CRT (4:3 display). There are black bars on either side and above/below the picture (around 3 inches wide each). That's a lot of picture real estate to lose! The full image is there, just shrunk. I have confirmed that the decoder is set to output 4:3 Letterbox, as my first thought was that this setting had been changed somehow.
It only ever happens (to the best of my knowledge) on these 2 channels, but it isn't always like that.
Have Sky changed something in the way they broadcast TV3 and Nat Geo or is there a potential problem with my decoder?