As it stands, for quick reply:
1. You're viewing categories.aspx and click on a thread.
2. messageview.aspx submits form data to messagepost.aspx
3. messagepost.aspx reads the form element 'quickreply' and sees a value of 'yes'.
4. messagepost.aspx sends you back to a new copy of messageview.aspx.
Clicking 'Back' from #4 to get to #1 would mean somehow rewriting the client side (ie. browser) URL tracking system. In fact it can be done by creative use of IFRAMEs or somesuch, but it really isn't worth the bother.