I don't know why the "back" button may not be working, but if it isn't, one way to avoid having to go through the "tree" to get to where you were is to use the right click instead of the left click.

When you want to view a posting (or a topic), instead of clicking on it normally ("left clicking"), use the "right click". It brings a drop-down menu. Select "open in new window". Read the posting in the new window, then close the window and you're back where you were before clicking.