Tim saw every image of an open conversation vanish and come back about twice a second for a while, then stop. The images go only when the reader makes the thread's view again, since a new view loads them again; updating one keeps them. That did not happen with the same mail on a test server, and nothing recorded what made the view again on his machine. The reader now says so at info, with the thread, how many messages it has, and why: it was opened, its messages came, or the reader opened again. The log file keeps the reader's info lines, as it does the session's, so the next time it happens the cause is on disk.