It's probably intentional to form a single common. I deal with dataloggers (from weather stations) and all of our various signals come together to a common bus. It's not unusual at all. That being said, I don't claim to be an expert at all when it comes to the insides of a/v gear. I would imagine the principles are the same, but I don't know what kinds of interference may be introduced that wouldn't bother the kinds of applications I'm using that may be detrimental to here.