Last night I had a problem with the sound on BBC 1 HD. At the time it was just connected via the HDMI cable, apparently it was a BBC fault.
To day I thought I'd try reconnect my Tivo box sound through my blu-ray and it's 5.1 surround sound using an optical cable. All the channels work fine except BBC 1 HD which is completely silent, even with the volume turned up full. Playing the sound through the TV no problem (apart from being slightly quieter).