Yep, I don't think there is anything that can be done about that. An offline mode person will also have a yellow dot instead of a green one on their posts
Oh good question! The reason why you see people (such as myself) as offline is because we've put ourselves on offline mode. We can browse the forum without anyone knowing we are on. To put yourself on offline mode, or take yourself off just click Settings > General Settings > and then at the top click Invisible mode ON/Off and > Save Changes