It works that way on stackoverflow, reddit and many other popular websites. (try to add test comment to this question, then navigate to different page and hit back button to come back - your comment will be "gone")
This makes sense, yet some websites (apple.com, basecamphq.com etc) are somehow forcing browser to serve user the latest state of the page. (go to http://www.apple.com/ca/search/?q=ipod,
click on say Downloads link at the top and then click back button - all DOM updates will be preserved)
where is the inconsistency coming from?