I read to the end of a thread, replied, pressed cmd-K, and in the top pane the thread went bold and got a (1) but in the left pane my post didn't get added to the thread.
Clicking on the subject in the top pane updated the left pane thread to include my post.
Pressing "Get all Latest" does correctly update the left pane, so it may be just cmd-K that doesn't trigger a redraw.