Confirmation of operation of marking posts as read please. (from Options Menu)

[#1]

In the 'Options' popup menu there are two options mark as New and mark as Read. Now taking this literally does that mean that ALL new posts that have arrived after the page is loaded are marked as read when this option is selected?

For example, I land on the page using this : https://community.plus.net/t5/forums/unreadpostspage/tab/message:full

There are 12 messages so I go and get a cup of coffee, in the meantime 5 more posts arrive (but I don't know this), I then read the original 12 posts and select mark as read from the Options. Does this then mark the 17 messages as read, even though I have missed 5 of them?

[#2]

I believe it would mark all the posts on that page as read. However reading the threads would also mark the particular threads as read. If you then refresh the page, that would update it and show you the 5 you've missed.

[#3]

OK, I've just tested this and it does in fact mark ALL posts as read including ones that arrive during the 'reading' of the content. Using another machine and browser (not logged in) I saw a post arriving in Broadband regarding massive usage. I then marked all the posts as read, and on return it did not show me any missed posts. Doing a refresh using the link I posted earlier it too maintains there are no new post, which is in fact wrong, which is what I suspected all along.