Yeah, that is a frustrating thing. But it's probably the same deal - the input chip triggers on a video input, and doesn't pass anything until it sees that video signal. It's a cheap way of keeping the rest of the system blanked until the main component, the video signal, is present. It probably originally was related to power saving, but now is just built in because that stuff gets copied over and over without the manufacturer understanding why it was put there in the first place.