This is probably because the Zone 2 TV is not able to decode multi-channel audio. TV adverts are broadcast in stereo, but many satellite programs/films are broadcast in 5.1 multi-channel.
If you have HDMI connected to a Zone 2 TV, when setting the Zone 2 Source to any source that is the different from the main zone, the ‘raw’ audio and video will be sent into Zone 2, as output by the source. If the selected Zone 2 Source has a multi-channel audio signal (eg. BD player/5.1 satellite signal) the Zone 2 TV must be able to play/decode multi-channel HDMI audio, otherwise, no sound will be heard in this case.
We recommend that the Zone 2 TV is able to play/decode multi-channel HDMI audio. If not, then for multi-channel audio sources, only the picture will be displayed in Zone 2 (unless using the Follow Main feature).