>I am not sure what that means, but all I can say it everyday I notice threads half started, without me seeing the original post. I don't know how that happens, but it does.
What you get is the new messages. A message can be either a thread (top message of a thread) or a message within it. Thus, a first message of a thread is the top layer of it. Underneath can be several layers of messages. So, among new messages can be new threads, where you will see the first message of a thread, or ongoing thread messages, where you will see new messages from the related threads.
Thus, if you have already read the first message of a thread, it will not appear in the next refresh or at the next login.
When reading a message, as previously mentioned, if this is not the top message of the thread, which usually starts with RE:, there will be a hyperlink in the thread title, when viewing the message, to jump back to the original message if you wish to do so.
Let me know if you need more information.