Kit,
I am sorry no one has responded to you and it's been over a month. I anticipate the correct answer is that this is "performing as intended" because I see this exact behavior on multiple versions of the LN client on Windows XP, Windows 7, and RHEL 5.x. I see one key advantage in that I can tell at-a-glance if I have received a ST message because the icon changes. It also lets you know you have completed and closed all chat windows (by reverting, as you noted). I do understand your concern. I am not aware if there is a setting to change this. Perhaps someone else will notice this post and respond.
Good Luck!