Reply form missing?

I'm not sure this is an issue or my sleep-deprived brain playing tricks on me so I'm happy to delete this issue if someone can enlighten me.

Using the 1.x release I could swear there used to be a 'reply' area underneath the current message threads that would then update the thread with the new message using ajax. This reply area has disappeared (after I decided to reinstall) so a user has to create a new message to the same user in order to reply instead of staying on the same page. I can't find a mention of this reply form anywhere online. 

Is there a step I've missed to have this form appear on the page?

Thanks and apologies if I've posted this in the wrong place.