Unread oldest "New Posts" threads get marked as read
 

The New Posts button brings a list of something on the order of 150 threads on 5 pages, where older ones may be marked as not new but having unread posts.

From one to several threads at the end of the list will, without reading, lose that bold highlighting which normally indicates the threads read during the current session. (More thread titles lose the bold as session time increases...7 today when I started typing this post; 8 when finished; and a click then for "New Posts" brings a thread title list that is shorter because these un-bolded end-of-list threads have been deleted.)

What phenomena or entity is performing the un-bolding? Why?

Anyone else notice such?