You've never been allowed to post a topic without a title, and now if you send a mail without a subject, it'll be "No Subject"
As far as the forum highlighting goes, yes, it's supposed to disappear for all threads when you visit the board's main page. Doing it otherwise would require an entry in the database that ties together every person with every thread.. It'd slow things down and take up way too much space. Not going to happen. Just remember what was highlighted if you don't use tabs