That is related to our instant search, where you don't need to hit the return key to search. This causes the problem, that we need to identify when a query ends and the next query starts, to create the correct entries for the back button. We do this via timing - if the pause between key presses is too long, a new, separate entry is assumed. As the DeepHN is a single dynamic HTML page, we need to implement and manage the browser navigation logic ourselves.