Not sure if anyone has noticed, but the 'SUBJECT' line is missing when a reply to a post is made.
Once upon a time a person could reply in a thread, but still change the subject line somewhat in order to make a point more clearly. The field for the subject line is still in the Compose Message window, but once 'Submit' is clicked it's gone.

I had not noticed this until I tried it myself in a post in the Gay Thailand Forum. Most of the time the original post's title still lives within the subject line of every reply by default, but in fact a poster can change it if he wishes ... for instance if one is attempting to make a joke within an overly-serious thread.

A small item I know, but the subject line has always been there, available to be changed and then show up in the posted reply.