timeline.js: StatusContainer: max_id query param for POST ack.json is set only when too many unacked statuses are loaded (and there may be remaining unacked statuses not loaded). This is because setting max_id for POST ack.json can lead to acknowledging unread statuses, and thus should be avoided as much as possible. However, if there are too many unacked statuses, it is inevitable to use max_id param to collectively acknowledge part of them.