Reopened tabs (Cmd + Shift + T) should retain their back history - right now they are restored without any history.
Open a tab, browse a few pages. Open a second tab, close the first tab. Realise you didn't want to do that - reopen original tab via Cmd + Shift + T. Tab is restored, but the back button doesn't go anywhere, as there's no back stack available.
Firefox and Safari both do this.