When I sent a private message to my husband, it showed up in my main stream, and his, I assume. That's all I know. I just would prefer it be empty and let me decide, on every message, who I want to send it to. That way, I don't ACCIDENTALLY send to a circle I didn't intend. I just know that if it's a detail I can skip, I will make the mistake. If I have to choose before I can send, I will get it right.