I have attached a screen grab to show long user names looks messy and to ask what the check box is for?
and to ask what the check box is for?
Did you try checking it? It selects all the posts in that section, on that page. It can be used in conjunction with the drop down menu to mark some unread posts as read, rather than marking all unread posts as read.
Although that option no longer actually works. Check a single post, and select to mark it as read, and ALL posts in that forum get marked as read.
I'm not keen on clicking unknown boxes as with the current state of the forum it may have declared thermonuclear war with someone by launching a game of ticktacktoe.