When the scroll position is at the bottom while reducing the app window size, the message list moves down. In that case it should stay at the bottom. If the scroll position is not at the bottom, I would probably try to maintain the current (upper) y-position unless the content becomes too short to fill the whole area, in which case it should move down.
When the scroll position is at the bottom while reducing the app window size, the message list moves down. In that case it should stay at the bottom. If the scroll position is not at the bottom, I would probably try to maintain the current (upper) y-position unless the content becomes too short to fill the whole area, in which case it should move down.