I am chatting with someone or in a multiuserchat and scrolling back through the chat, if a new message arrives the view is pushed back down to the bottom to show the new message. So my request is two fold and people may or may not agree with either.
At least when I am holding the mouse down somewhere on the scroll bar, don’'t return the view to the bottom. If I am scrolling back through trying to find something it can be very confusing if the view keeps popping back to the bottom.
The second request would be the same if I am viewing an older part of the chat and not holding down the mouse button, o keep the focus there until I return the scroll bar to the bottom of the screen.