If you're on site foo, then go to bar, then baz, then bar again. The history GUI, whether the sidebar or the history manager (Ctrl-Shift-h), is not going to show foo, bar, baz, bar. It's going to show foo, baz, bar. The first time you went to bar is hidden. It's present in the DB, but no part of the GUI AFAICT is going to mention a visit to bar between visits to foo and baz.